Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
patch that shrunk the kvm_lock critical section so that the mmu_lock
critical section does not nest with it, but in the end there is no reason
for the vm_list to be protected by a raw spinlock. Only manipulations
of kvm_usage_count and the consequent hardware_enable/disable operations
are not preemptable.
This small series thus splits the kvm_lock in the "raw" part and the
"non-raw" part.
Paul, could you please provide your Tested-by?
Thanks,
Paolo
Paolo Bonzini (3):
KVM: cleanup (physical) CPU hotplug
KVM: protect kvm_usage_count with its own spinlock
KVM: Convert kvm_lock back to non-raw spinlock
Documentation/virtual/kvm/locking.txt | 8 ++++--
arch/x86/kvm/mmu.c | 4 +--
arch/x86/kvm/x86.c | 8 +++---
include/linux/kvm_host.h | 2 +-
virt/kvm/kvm_main.c | 51 ++++++++++++++++++-----------------
5 files changed, 40 insertions(+), 33 deletions(-)
--
1.8.3.1
Remove the useless argument, and do not do anything if there are no
VMs running at the time of the hotplug.
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>
---
virt/kvm/kvm_main.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 979bff4..75522b3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2681,10 +2681,11 @@ static void hardware_enable_nolock(void *junk)
}
}
-static void hardware_enable(void *junk)
+static void hardware_enable(void)
{
raw_spin_lock(&kvm_lock);
- hardware_enable_nolock(junk);
+ if (kvm_usage_count)
+ hardware_enable_nolock(NULL);
raw_spin_unlock(&kvm_lock);
}
@@ -2698,10 +2699,11 @@ static void hardware_disable_nolock(void *junk)
kvm_arch_hardware_disable(NULL);
}
-static void hardware_disable(void *junk)
+static void hardware_disable(void)
{
raw_spin_lock(&kvm_lock);
- hardware_disable_nolock(junk);
+ if (kvm_usage_count)
+ hardware_disable_nolock(NULL);
raw_spin_unlock(&kvm_lock);
}
@@ -2756,12 +2758,12 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
case CPU_DYING:
printk(KERN_INFO "kvm: disabling virtualization on CPU%d\n",
cpu);
- hardware_disable(NULL);
+ hardware_disable();
break;
case CPU_STARTING:
printk(KERN_INFO "kvm: enabling virtualization on CPU%d\n",
cpu);
- hardware_enable(NULL);
+ hardware_enable();
break;
}
return NOTIFY_OK;
--
1.8.3.1
In commit e935b8372cf8 ("KVM: Convert kvm_lock to raw_spinlock"),
the kvm_lock was made a raw lock. However, the kvm mmu_shrink()
function tries to grab the (non-raw) mmu_lock within the scope of
the raw locked kvm_lock being held. This leads to the following:
BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 0, pid: 55, name: kswapd0
Preemption disabled at:[<ffffffffa0376eac>] mmu_shrink+0x5c/0x1b0 [kvm]
Pid: 55, comm: kswapd0 Not tainted 3.4.34_preempt-rt
Call Trace:
[<ffffffff8106f2ad>] __might_sleep+0xfd/0x160
[<ffffffff817d8d64>] rt_spin_lock+0x24/0x50
[<ffffffffa0376f3c>] mmu_shrink+0xec/0x1b0 [kvm]
[<ffffffff8111455d>] shrink_slab+0x17d/0x3a0
[<ffffffff81151f00>] ? mem_cgroup_iter+0x130/0x260
[<ffffffff8111824a>] balance_pgdat+0x54a/0x730
[<ffffffff8111fe47>] ? set_pgdat_percpu_threshold+0xa7/0xd0
[<ffffffff811185bf>] kswapd+0x18f/0x490
[<ffffffff81070961>] ? get_parent_ip+0x11/0x50
[<ffffffff81061970>] ? __init_waitqueue_head+0x50/0x50
[<ffffffff81118430>] ? balance_pgdat+0x730/0x730
[<ffffffff81060d2b>] kthread+0xdb/0xe0
[<ffffffff8106e122>] ? finish_task_switch+0x52/0x100
[<ffffffff817e1e94>] kernel_thread_helper+0x4/0x10
[<ffffffff81060c50>] ? __init_kthread_worker+0x
After the previous patch, kvm_lock need not be a raw spinlock anymore,
so change it back.
Reported-by: Paul Gortmaker <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>
---
Documentation/virtual/kvm/locking.txt | 2 +-
arch/x86/kvm/mmu.c | 4 ++--
arch/x86/kvm/x86.c | 8 ++++----
include/linux/kvm_host.h | 2 +-
virt/kvm/kvm_main.c | 18 +++++++++---------
5 files changed, 17 insertions(+), 17 deletions(-)
diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
index ba9e1c2..f886941 100644
--- a/Documentation/virtual/kvm/locking.txt
+++ b/Documentation/virtual/kvm/locking.txt
@@ -132,7 +132,7 @@ See the comments in spte_has_volatile_bits() and mmu_spte_update().
------------
Name: kvm_lock
-Type: raw_spinlock
+Type: spinlock_t
Arch: any
Protects: - vm_list
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 6e2d2c8..d027a72 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4429,7 +4429,7 @@ static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
if (nr_to_scan == 0)
goto out;
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_for_each_entry(kvm, &vm_list, vm_list) {
int idx;
@@ -4473,7 +4473,7 @@ unlock:
break;
}
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
out:
return percpu_counter_read_positive(&kvm_total_used_mmu_pages);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7c36099..3acd631 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5273,7 +5273,7 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va
smp_call_function_single(freq->cpu, tsc_khz_changed, freq, 1);
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_for_each_entry(kvm, &vm_list, vm_list) {
kvm_for_each_vcpu(i, vcpu, kvm) {
if (vcpu->cpu != freq->cpu)
@@ -5283,7 +5283,7 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va
send_ipi = 1;
}
}
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
if (freq->old < freq->new && send_ipi) {
/*
@@ -5436,12 +5436,12 @@ static void pvclock_gtod_update_fn(struct work_struct *work)
struct kvm_vcpu *vcpu;
int i;
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_for_each_entry(kvm, &vm_list, vm_list)
kvm_for_each_vcpu(i, vcpu, kvm)
set_bit(KVM_REQ_MASTERCLOCK_UPDATE, &vcpu->requests);
atomic_set(&kvm_guest_has_master_clock, 0);
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
}
static DECLARE_WORK(pvclock_gtod_work, pvclock_gtod_update_fn);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 749bdb1..7c961e1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -142,7 +142,7 @@ struct kvm;
struct kvm_vcpu;
extern struct kmem_cache *kvm_vcpu_cache;
-extern raw_spinlock_t kvm_lock;
+extern spinlock_t kvm_lock;
extern struct list_head vm_list;
struct kvm_io_range {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index da13379..3397a9c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -70,7 +70,7 @@ MODULE_LICENSE("GPL");
* kvm->lock --> kvm->slots_lock --> kvm->irq_lock
*/
-DEFINE_RAW_SPINLOCK(kvm_lock);
+DEFINE_SPINLOCK(kvm_lock);
static DEFINE_RAW_SPINLOCK(kvm_count_lock);
LIST_HEAD(vm_list);
@@ -491,9 +491,9 @@ static struct kvm *kvm_create_vm(unsigned long type)
if (r)
goto out_err;
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_add(&kvm->vm_list, &vm_list);
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
return kvm;
@@ -582,9 +582,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
struct mm_struct *mm = kvm->mm;
kvm_arch_sync_events(kvm);
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_del(&kvm->vm_list);
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
kvm_free_irq_routing(kvm);
for (i = 0; i < KVM_NR_BUSES; i++)
kvm_io_bus_destroy(kvm->buses[i]);
@@ -3057,10 +3057,10 @@ static int vm_stat_get(void *_offset, u64 *val)
struct kvm *kvm;
*val = 0;
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_for_each_entry(kvm, &vm_list, vm_list)
*val += *(u32 *)((void *)kvm + offset);
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
return 0;
}
@@ -3074,12 +3074,12 @@ static int vcpu_stat_get(void *_offset, u64 *val)
int i;
*val = 0;
- raw_spin_lock(&kvm_lock);
+ spin_lock(&kvm_lock);
list_for_each_entry(kvm, &vm_list, vm_list)
kvm_for_each_vcpu(i, vcpu, kvm)
*val += *(u32 *)((void *)vcpu + offset);
- raw_spin_unlock(&kvm_lock);
+ spin_unlock(&kvm_lock);
return 0;
}
--
1.8.3.1
The VM list need not be protected by a raw spinlock. Separate the
two so that kvm_lock can be made non-raw.
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>
---
Documentation/virtual/kvm/locking.txt | 6 +++++-
virt/kvm/kvm_main.c | 19 ++++++++++---------
2 files changed, 15 insertions(+), 10 deletions(-)
diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
index a9f366e..ba9e1c2 100644
--- a/Documentation/virtual/kvm/locking.txt
+++ b/Documentation/virtual/kvm/locking.txt
@@ -135,7 +135,11 @@ Name: kvm_lock
Type: raw_spinlock
Arch: any
Protects: - vm_list
- - hardware virtualization enable/disable
+
+Name: kvm_count_lock
+Type: raw_spinlock_t
+Arch: any
+Protects: - hardware virtualization enable/disable
Comment: 'raw' because hardware enabling/disabling must be atomic /wrt
migration.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 75522b3..da13379 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -71,6 +71,7 @@ MODULE_LICENSE("GPL");
*/
DEFINE_RAW_SPINLOCK(kvm_lock);
+static DEFINE_RAW_SPINLOCK(kvm_count_lock);
LIST_HEAD(vm_list);
static cpumask_var_t cpus_hardware_enabled;
@@ -2683,10 +2684,10 @@ static void hardware_enable_nolock(void *junk)
static void hardware_enable(void)
{
- raw_spin_lock(&kvm_lock);
+ raw_spin_lock(&kvm_count_lock);
if (kvm_usage_count)
hardware_enable_nolock(NULL);
- raw_spin_unlock(&kvm_lock);
+ raw_spin_unlock(&kvm_count_lock);
}
static void hardware_disable_nolock(void *junk)
@@ -2701,10 +2702,10 @@ static void hardware_disable_nolock(void *junk)
static void hardware_disable(void)
{
- raw_spin_lock(&kvm_lock);
+ raw_spin_lock(&kvm_count_lock);
if (kvm_usage_count)
hardware_disable_nolock(NULL);
- raw_spin_unlock(&kvm_lock);
+ raw_spin_unlock(&kvm_count_lock);
}
static void hardware_disable_all_nolock(void)
@@ -2718,16 +2719,16 @@ static void hardware_disable_all_nolock(void)
static void hardware_disable_all(void)
{
- raw_spin_lock(&kvm_lock);
+ raw_spin_lock(&kvm_count_lock);
hardware_disable_all_nolock();
- raw_spin_unlock(&kvm_lock);
+ raw_spin_unlock(&kvm_count_lock);
}
static int hardware_enable_all(void)
{
int r = 0;
- raw_spin_lock(&kvm_lock);
+ raw_spin_lock(&kvm_count_lock);
kvm_usage_count++;
if (kvm_usage_count == 1) {
@@ -2740,7 +2741,7 @@ static int hardware_enable_all(void)
}
}
- raw_spin_unlock(&kvm_lock);
+ raw_spin_unlock(&kvm_count_lock);
return r;
}
@@ -3133,7 +3134,7 @@ static int kvm_suspend(void)
static void kvm_resume(void)
{
if (kvm_usage_count) {
- WARN_ON(raw_spin_is_locked(&kvm_lock));
+ WARN_ON(raw_spin_is_locked(&kvm_count_lock));
hardware_enable_nolock(NULL);
}
}
--
1.8.3.1
On 13-09-16 10:06 AM, Paolo Bonzini wrote:
> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> patch that shrunk the kvm_lock critical section so that the mmu_lock
> critical section does not nest with it, but in the end there is no reason
> for the vm_list to be protected by a raw spinlock. Only manipulations
> of kvm_usage_count and the consequent hardware_enable/disable operations
> are not preemptable.
>
> This small series thus splits the kvm_lock in the "raw" part and the
> "non-raw" part.
>
> Paul, could you please provide your Tested-by?
Sure, I'll go back and see if I can find what triggered it in the
original report, and give the patches a spin on 3.4.x-rt (and probably
3.10.x-rt, since that is where rt-current is presently).
Paul.
--
>
> Thanks,
>
> Paolo
>
> Paolo Bonzini (3):
> KVM: cleanup (physical) CPU hotplug
> KVM: protect kvm_usage_count with its own spinlock
> KVM: Convert kvm_lock back to non-raw spinlock
>
> Documentation/virtual/kvm/locking.txt | 8 ++++--
> arch/x86/kvm/mmu.c | 4 +--
> arch/x86/kvm/x86.c | 8 +++---
> include/linux/kvm_host.h | 2 +-
> virt/kvm/kvm_main.c | 51 ++++++++++++++++++-----------------
> 5 files changed, 40 insertions(+), 33 deletions(-)
>
On 2013-09-16 16:06, Paolo Bonzini wrote:
> Remove the useless argument, and do not do anything if there are no
> VMs running at the time of the hotplug.
kvm_cpu_hotplug already filters !kvm_usage_count. If we need the check
to be under kvm_lock, drop that line as well. If that is not required
(machine still halted?), drop the related changes here.
Jan
>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> virt/kvm/kvm_main.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 979bff4..75522b3 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2681,10 +2681,11 @@ static void hardware_enable_nolock(void *junk)
> }
> }
>
> -static void hardware_enable(void *junk)
> +static void hardware_enable(void)
> {
> raw_spin_lock(&kvm_lock);
> - hardware_enable_nolock(junk);
> + if (kvm_usage_count)
> + hardware_enable_nolock(NULL);
> raw_spin_unlock(&kvm_lock);
> }
>
> @@ -2698,10 +2699,11 @@ static void hardware_disable_nolock(void *junk)
> kvm_arch_hardware_disable(NULL);
> }
>
> -static void hardware_disable(void *junk)
> +static void hardware_disable(void)
> {
> raw_spin_lock(&kvm_lock);
> - hardware_disable_nolock(junk);
> + if (kvm_usage_count)
> + hardware_disable_nolock(NULL);
> raw_spin_unlock(&kvm_lock);
> }
>
> @@ -2756,12 +2758,12 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
> case CPU_DYING:
> printk(KERN_INFO "kvm: disabling virtualization on CPU%d\n",
> cpu);
> - hardware_disable(NULL);
> + hardware_disable();
> break;
> case CPU_STARTING:
> printk(KERN_INFO "kvm: enabling virtualization on CPU%d\n",
> cpu);
> - hardware_enable(NULL);
> + hardware_enable();
> break;
> }
> return NOTIFY_OK;
>
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
Il 17/09/2013 09:57, Jan Kiszka ha scritto:
>> > Remove the useless argument, and do not do anything if there are no
>> > VMs running at the time of the hotplug.
> kvm_cpu_hotplug already filters !kvm_usage_count. If we need the check
> to be under kvm_lock, drop that line as well. If that is not required
> (machine still halted?), drop the related changes here.
CPU_DYING is called under stop_machine, CPU_STARTING is not. So I
should drop the test in kvm_cpu_hotplug. It's a bit clearer anyway to
not rely on stop_machine.
Paolo
[Re: [PATCH 0/3] KVM: Make kvm_lock non-raw] On 16/09/2013 (Mon 18:12) Paul Gortmaker wrote:
> On 13-09-16 10:06 AM, Paolo Bonzini wrote:
> > Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> > mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> > patch that shrunk the kvm_lock critical section so that the mmu_lock
> > critical section does not nest with it, but in the end there is no reason
> > for the vm_list to be protected by a raw spinlock. Only manipulations
> > of kvm_usage_count and the consequent hardware_enable/disable operations
> > are not preemptable.
> >
> > This small series thus splits the kvm_lock in the "raw" part and the
> > "non-raw" part.
> >
> > Paul, could you please provide your Tested-by?
>
> Sure, I'll go back and see if I can find what triggered it in the
> original report, and give the patches a spin on 3.4.x-rt (and probably
> 3.10.x-rt, since that is where rt-current is presently).
Seems fine on 3.4-rt. On 3.10.10-rt7 it looks like there are other
issues, probably not explicitly related to this patchset (see below).
Paul.
--
e1000e 0000:00:19.0 eth1: removed PHC
assign device 0:0:19.0
pci 0000:00:19.0: irq 43 for MSI/MSI-X
pci 0000:00:19.0: irq 43 for MSI/MSI-X
pci 0000:00:19.0: irq 43 for MSI/MSI-X
pci 0000:00:19.0: irq 43 for MSI/MSI-X
BUG: sleeping function called from invalid context at /home/paul/git/linux-rt/kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
2 locks held by swapper/0/0:
#0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
#1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
irq event stamp: 6121390
hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
softirqs last enabled at (0): [< (null)>] (null)
softirqs last disabled at (0): [< (null)>] (null)
Preemption disabled at:[<ffffffff810ebb9a>] cpu_startup_entry+0x1ba/0x430
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
ffffffff8201c440 ffff880223603cf0 ffffffff819f177d ffff880223603d18
ffffffff810c90d3 ffff880214a50110 0000000000000001 0000000000000001
ffff880223603d38 ffffffff819f89a4 ffff880214a50110 ffff880214a50110
Call Trace:
<IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
[<ffffffff810c90d3>] __might_sleep+0x153/0x250
[<ffffffff819f89a4>] rt_spin_lock+0x24/0x60
[<ffffffff810ccdd6>] __wake_up+0x36/0x70
[<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
[<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
[<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
[<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
[<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
[<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
[<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
[<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
[<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff8113cec8>] handle_irq_event+0x48/0x70
[<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
[<ffffffff8104c6ae>] handle_irq+0x1e/0x30
[<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
[<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
<EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
[<ffffffff819db767>] rest_init+0x137/0x140
[<ffffffff819db635>] ? rest_init+0x5/0x140
[<ffffffff822fde18>] start_kernel+0x3af/0x3bc
[<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
[<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
[<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
=================================
[ INFO: inconsistent lock state ]
3.10.10-rt7 #2 Not tainted
---------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
(&(&(&q->lock)->lock)->wait_lock){?.+.-.}, at: [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
{HARDIRQ-ON-W} state was registered at:
[<ffffffff810fc94d>] __lock_acquire+0x69d/0x20e0
[<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
[<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
[<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
[<ffffffff810ccdd6>] __wake_up+0x36/0x70
[<ffffffff8109c5ce>] run_timer_softirq+0x1be/0x390
[<ffffffff81092a09>] do_current_softirqs+0x239/0x5b0
[<ffffffff81092db8>] run_ksoftirqd+0x38/0x60
[<ffffffff810c5d7c>] smpboot_thread_fn+0x22c/0x340
[<ffffffff810bbf4d>] kthread+0xcd/0xe0
[<ffffffff81a019dc>] ret_from_fork+0x7c/0xb0
irq event stamp: 6121390
hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
softirqs last enabled at (0): [< (null)>] (null)
softirqs last disabled at (0): [< (null)>] (null)
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&(&(&q->lock)->lock)->wait_lock);
<Interrupt>
lock(&(&(&q->lock)->lock)->wait_lock);
*** DEADLOCK ***
2 locks held by swapper/0/0:
#0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
#1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
ffffffff8262b550 ffff880223603a40 ffffffff819f177d ffff880223603a90
ffffffff819ec532 0000000000000000 ffffffff00000000 ffff880200000001
0000000000000002 ffffffff8201ccc0 ffffffff810f9040 0000000000000000
Call Trace:
<IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
[<ffffffff819ec532>] print_usage_bug.part.36+0x28b/0x29a
[<ffffffff810f9040>] ? check_usage_backwards+0x150/0x150
[<ffffffff810f9dab>] mark_lock+0x28b/0x6a0
[<ffffffff810fcbf9>] __lock_acquire+0x949/0x20e0
[<ffffffff811091f2>] ? __module_text_address+0x12/0x60
[<ffffffff8110ea8f>] ? is_module_text_address+0x2f/0x60
[<ffffffff810b8408>] ? __kernel_text_address+0x58/0x80
[<ffffffff8104dbb2>] ? print_context_stack+0x62/0xf0
[<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
[<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
[<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
[<ffffffff810ccdd6>] __wake_up+0x36/0x70
[<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
[<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
[<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
[<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
[<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
[<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
[<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
[<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
[<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff8113cec8>] handle_irq_event+0x48/0x70
[<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
[<ffffffff8104c6ae>] handle_irq+0x1e/0x30
[<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
[<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
<EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
[<ffffffff819db767>] rest_init+0x137/0x140
[<ffffffff819db635>] ? rest_init+0x5/0x140
[<ffffffff822fde18>] start_kernel+0x3af/0x3bc
[<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
[<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
[<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
>
> Paul.
> --
>
> >
> > Thanks,
> >
> > Paolo
> >
> > Paolo Bonzini (3):
> > KVM: cleanup (physical) CPU hotplug
> > KVM: protect kvm_usage_count with its own spinlock
> > KVM: Convert kvm_lock back to non-raw spinlock
> >
> > Documentation/virtual/kvm/locking.txt | 8 ++++--
> > arch/x86/kvm/mmu.c | 4 +--
> > arch/x86/kvm/x86.c | 8 +++---
> > include/linux/kvm_host.h | 2 +-
> > virt/kvm/kvm_main.c | 51 ++++++++++++++++++-----------------
> > 5 files changed, 40 insertions(+), 33 deletions(-)
> >
On 2013-09-20 19:51, Paul Gortmaker wrote:
> [Re: [PATCH 0/3] KVM: Make kvm_lock non-raw] On 16/09/2013 (Mon 18:12) Paul Gortmaker wrote:
>
>> On 13-09-16 10:06 AM, Paolo Bonzini wrote:
>>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
>>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
>>> patch that shrunk the kvm_lock critical section so that the mmu_lock
>>> critical section does not nest with it, but in the end there is no reason
>>> for the vm_list to be protected by a raw spinlock. Only manipulations
>>> of kvm_usage_count and the consequent hardware_enable/disable operations
>>> are not preemptable.
>>>
>>> This small series thus splits the kvm_lock in the "raw" part and the
>>> "non-raw" part.
>>>
>>> Paul, could you please provide your Tested-by?
>>
>> Sure, I'll go back and see if I can find what triggered it in the
>> original report, and give the patches a spin on 3.4.x-rt (and probably
>> 3.10.x-rt, since that is where rt-current is presently).
>
> Seems fine on 3.4-rt. On 3.10.10-rt7 it looks like there are other
> issues, probably not explicitly related to this patchset (see below).
>
> Paul.
> --
>
> e1000e 0000:00:19.0 eth1: removed PHC
> assign device 0:0:19.0
> pci 0000:00:19.0: irq 43 for MSI/MSI-X
> pci 0000:00:19.0: irq 43 for MSI/MSI-X
> pci 0000:00:19.0: irq 43 for MSI/MSI-X
> pci 0000:00:19.0: irq 43 for MSI/MSI-X
> BUG: sleeping function called from invalid context at /home/paul/git/linux-rt/kernel/rtmutex.c:659
> in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
> 2 locks held by swapper/0/0:
> #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
> #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> irq event stamp: 6121390
> hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
> hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
> softirqs last enabled at (0): [< (null)>] (null)
> softirqs last disabled at (0): [< (null)>] (null)
> Preemption disabled at:[<ffffffff810ebb9a>] cpu_startup_entry+0x1ba/0x430
>
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
> Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
> ffffffff8201c440 ffff880223603cf0 ffffffff819f177d ffff880223603d18
> ffffffff810c90d3 ffff880214a50110 0000000000000001 0000000000000001
> ffff880223603d38 ffffffff819f89a4 ffff880214a50110 ffff880214a50110
> Call Trace:
> <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
> [<ffffffff810c90d3>] __might_sleep+0x153/0x250
> [<ffffffff819f89a4>] rt_spin_lock+0x24/0x60
> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
> [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
-rt lacks an atomic waitqueue for triggering VCPU wakeups on MSIs from
assigned devices directly from the host IRQ handler. We need to disable
this fast-path in -rt or introduce such an abstraction (I did this once
over 2.6.33-rt).
IIRC, VFIO goes the slower patch via a kernel thread unconditionally,
thus cannot trigger this. Only legacy device assignment is affected.
Jan
> [<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
> [<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
> [<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
> [<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> [<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
> [<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
> [<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
> [<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> [<ffffffff8113cec8>] handle_irq_event+0x48/0x70
> [<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
> [<ffffffff8104c6ae>] handle_irq+0x1e/0x30
> [<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
> [<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
> <EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> [<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
> [<ffffffff819db767>] rest_init+0x137/0x140
> [<ffffffff819db635>] ? rest_init+0x5/0x140
> [<ffffffff822fde18>] start_kernel+0x3af/0x3bc
> [<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
> [<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
> [<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
>
> =================================
> [ INFO: inconsistent lock state ]
> 3.10.10-rt7 #2 Not tainted
> ---------------------------------
> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
> (&(&(&q->lock)->lock)->wait_lock){?.+.-.}, at: [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
> {HARDIRQ-ON-W} state was registered at:
> [<ffffffff810fc94d>] __lock_acquire+0x69d/0x20e0
> [<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
> [<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
> [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
> [<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
> [<ffffffff8109c5ce>] run_timer_softirq+0x1be/0x390
> [<ffffffff81092a09>] do_current_softirqs+0x239/0x5b0
> [<ffffffff81092db8>] run_ksoftirqd+0x38/0x60
> [<ffffffff810c5d7c>] smpboot_thread_fn+0x22c/0x340
> [<ffffffff810bbf4d>] kthread+0xcd/0xe0
> [<ffffffff81a019dc>] ret_from_fork+0x7c/0xb0
> irq event stamp: 6121390
> hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
> hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
> softirqs last enabled at (0): [< (null)>] (null)
> softirqs last disabled at (0): [< (null)>] (null)
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(&(&(&q->lock)->lock)->wait_lock);
> <Interrupt>
> lock(&(&(&q->lock)->lock)->wait_lock);
>
> *** DEADLOCK ***
>
> 2 locks held by swapper/0/0:
> #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
> #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
>
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
> Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
> ffffffff8262b550 ffff880223603a40 ffffffff819f177d ffff880223603a90
> ffffffff819ec532 0000000000000000 ffffffff00000000 ffff880200000001
> 0000000000000002 ffffffff8201ccc0 ffffffff810f9040 0000000000000000
> Call Trace:
> <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
> [<ffffffff819ec532>] print_usage_bug.part.36+0x28b/0x29a
> [<ffffffff810f9040>] ? check_usage_backwards+0x150/0x150
> [<ffffffff810f9dab>] mark_lock+0x28b/0x6a0
> [<ffffffff810fcbf9>] __lock_acquire+0x949/0x20e0
> [<ffffffff811091f2>] ? __module_text_address+0x12/0x60
> [<ffffffff8110ea8f>] ? is_module_text_address+0x2f/0x60
> [<ffffffff810b8408>] ? __kernel_text_address+0x58/0x80
> [<ffffffff8104dbb2>] ? print_context_stack+0x62/0xf0
> [<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
> [<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
> [<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
> [<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
> [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
> [<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
> [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
> [<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
> [<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
> [<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
> [<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> [<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
> [<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
> [<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
> [<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> [<ffffffff8113cec8>] handle_irq_event+0x48/0x70
> [<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
> [<ffffffff8104c6ae>] handle_irq+0x1e/0x30
> [<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
> [<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
> <EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> [<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
> [<ffffffff819db767>] rest_init+0x137/0x140
> [<ffffffff819db635>] ? rest_init+0x5/0x140
> [<ffffffff822fde18>] start_kernel+0x3af/0x3bc
> [<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
> [<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
> [<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
On 13-09-20 02:04 PM, Jan Kiszka wrote:
> On 2013-09-20 19:51, Paul Gortmaker wrote:
>> [Re: [PATCH 0/3] KVM: Make kvm_lock non-raw] On 16/09/2013 (Mon 18:12) Paul Gortmaker wrote:
>>
>>> On 13-09-16 10:06 AM, Paolo Bonzini wrote:
>>>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
>>>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
>>>> patch that shrunk the kvm_lock critical section so that the mmu_lock
>>>> critical section does not nest with it, but in the end there is no reason
>>>> for the vm_list to be protected by a raw spinlock. Only manipulations
>>>> of kvm_usage_count and the consequent hardware_enable/disable operations
>>>> are not preemptable.
>>>>
>>>> This small series thus splits the kvm_lock in the "raw" part and the
>>>> "non-raw" part.
>>>>
>>>> Paul, could you please provide your Tested-by?
>>>
>>> Sure, I'll go back and see if I can find what triggered it in the
>>> original report, and give the patches a spin on 3.4.x-rt (and probably
>>> 3.10.x-rt, since that is where rt-current is presently).
>>
>> Seems fine on 3.4-rt. On 3.10.10-rt7 it looks like there are other
>> issues, probably not explicitly related to this patchset (see below).
>>
>> Paul.
>> --
>>
>> e1000e 0000:00:19.0 eth1: removed PHC
>> assign device 0:0:19.0
>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>> BUG: sleeping function called from invalid context at /home/paul/git/linux-rt/kernel/rtmutex.c:659
>> in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
>> 2 locks held by swapper/0/0:
>> #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
>> #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
>> irq event stamp: 6121390
>> hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
>> hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
>> softirqs last enabled at (0): [< (null)>] (null)
>> softirqs last disabled at (0): [< (null)>] (null)
>> Preemption disabled at:[<ffffffff810ebb9a>] cpu_startup_entry+0x1ba/0x430
>>
>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
>> Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
>> ffffffff8201c440 ffff880223603cf0 ffffffff819f177d ffff880223603d18
>> ffffffff810c90d3 ffff880214a50110 0000000000000001 0000000000000001
>> ffff880223603d38 ffffffff819f89a4 ffff880214a50110 ffff880214a50110
>> Call Trace:
>> <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
>> [<ffffffff810c90d3>] __might_sleep+0x153/0x250
>> [<ffffffff819f89a4>] rt_spin_lock+0x24/0x60
>> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
>> [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
>
> -rt lacks an atomic waitqueue for triggering VCPU wakeups on MSIs from
> assigned devices directly from the host IRQ handler. We need to disable
> this fast-path in -rt or introduce such an abstraction (I did this once
> over 2.6.33-rt).
Ah, right -- the simple wait queue support (currently -rt specific)
would have to be used here. It is on the todo list to get that moved
from -rt into mainline.
Paul.
--
>
> IIRC, VFIO goes the slower patch via a kernel thread unconditionally,
> thus cannot trigger this. Only legacy device assignment is affected.
>
> Jan
>
>> [<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
>> [<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
>> [<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
>> [<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
>> [<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
>> [<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
>> [<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
>> [<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
>> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
>> [<ffffffff8113cec8>] handle_irq_event+0x48/0x70
>> [<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
>> [<ffffffff8104c6ae>] handle_irq+0x1e/0x30
>> [<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
>> [<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
>> <EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
>> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
>> [<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
>> [<ffffffff819db767>] rest_init+0x137/0x140
>> [<ffffffff819db635>] ? rest_init+0x5/0x140
>> [<ffffffff822fde18>] start_kernel+0x3af/0x3bc
>> [<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
>> [<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
>> [<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
>>
>> =================================
>> [ INFO: inconsistent lock state ]
>> 3.10.10-rt7 #2 Not tainted
>> ---------------------------------
>> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
>> swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
>> (&(&(&q->lock)->lock)->wait_lock){?.+.-.}, at: [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
>> {HARDIRQ-ON-W} state was registered at:
>> [<ffffffff810fc94d>] __lock_acquire+0x69d/0x20e0
>> [<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
>> [<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
>> [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
>> [<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
>> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
>> [<ffffffff8109c5ce>] run_timer_softirq+0x1be/0x390
>> [<ffffffff81092a09>] do_current_softirqs+0x239/0x5b0
>> [<ffffffff81092db8>] run_ksoftirqd+0x38/0x60
>> [<ffffffff810c5d7c>] smpboot_thread_fn+0x22c/0x340
>> [<ffffffff810bbf4d>] kthread+0xcd/0xe0
>> [<ffffffff81a019dc>] ret_from_fork+0x7c/0xb0
>> irq event stamp: 6121390
>> hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
>> hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
>> softirqs last enabled at (0): [< (null)>] (null)
>> softirqs last disabled at (0): [< (null)>] (null)
>>
>> other info that might help us debug this:
>> Possible unsafe locking scenario:
>>
>> CPU0
>> ----
>> lock(&(&(&q->lock)->lock)->wait_lock);
>> <Interrupt>
>> lock(&(&(&q->lock)->lock)->wait_lock);
>>
>> *** DEADLOCK ***
>>
>> 2 locks held by swapper/0/0:
>> #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
>> #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
>>
>> stack backtrace:
>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
>> Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
>> ffffffff8262b550 ffff880223603a40 ffffffff819f177d ffff880223603a90
>> ffffffff819ec532 0000000000000000 ffffffff00000000 ffff880200000001
>> 0000000000000002 ffffffff8201ccc0 ffffffff810f9040 0000000000000000
>> Call Trace:
>> <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
>> [<ffffffff819ec532>] print_usage_bug.part.36+0x28b/0x29a
>> [<ffffffff810f9040>] ? check_usage_backwards+0x150/0x150
>> [<ffffffff810f9dab>] mark_lock+0x28b/0x6a0
>> [<ffffffff810fcbf9>] __lock_acquire+0x949/0x20e0
>> [<ffffffff811091f2>] ? __module_text_address+0x12/0x60
>> [<ffffffff8110ea8f>] ? is_module_text_address+0x2f/0x60
>> [<ffffffff810b8408>] ? __kernel_text_address+0x58/0x80
>> [<ffffffff8104dbb2>] ? print_context_stack+0x62/0xf0
>> [<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
>> [<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
>> [<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
>> [<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
>> [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
>> [<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
>> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
>> [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
>> [<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
>> [<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
>> [<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
>> [<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
>> [<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
>> [<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
>> [<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
>> [<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
>> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
>> [<ffffffff8113cec8>] handle_irq_event+0x48/0x70
>> [<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
>> [<ffffffff8104c6ae>] handle_irq+0x1e/0x30
>> [<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
>> [<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
>> <EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
>> [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
>> [<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
>> [<ffffffff819db767>] rest_init+0x137/0x140
>> [<ffffffff819db635>] ? rest_init+0x5/0x140
>> [<ffffffff822fde18>] start_kernel+0x3af/0x3bc
>> [<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
>> [<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
>> [<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
>
On 2013-09-20 20:18, Paul Gortmaker wrote:
> On 13-09-20 02:04 PM, Jan Kiszka wrote:
>> On 2013-09-20 19:51, Paul Gortmaker wrote:
>>> [Re: [PATCH 0/3] KVM: Make kvm_lock non-raw] On 16/09/2013 (Mon 18:12) Paul Gortmaker wrote:
>>>
>>>> On 13-09-16 10:06 AM, Paolo Bonzini wrote:
>>>>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
>>>>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
>>>>> patch that shrunk the kvm_lock critical section so that the mmu_lock
>>>>> critical section does not nest with it, but in the end there is no reason
>>>>> for the vm_list to be protected by a raw spinlock. Only manipulations
>>>>> of kvm_usage_count and the consequent hardware_enable/disable operations
>>>>> are not preemptable.
>>>>>
>>>>> This small series thus splits the kvm_lock in the "raw" part and the
>>>>> "non-raw" part.
>>>>>
>>>>> Paul, could you please provide your Tested-by?
>>>>
>>>> Sure, I'll go back and see if I can find what triggered it in the
>>>> original report, and give the patches a spin on 3.4.x-rt (and probably
>>>> 3.10.x-rt, since that is where rt-current is presently).
>>>
>>> Seems fine on 3.4-rt. On 3.10.10-rt7 it looks like there are other
>>> issues, probably not explicitly related to this patchset (see below).
>>>
>>> Paul.
>>> --
>>>
>>> e1000e 0000:00:19.0 eth1: removed PHC
>>> assign device 0:0:19.0
>>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>>> pci 0000:00:19.0: irq 43 for MSI/MSI-X
>>> BUG: sleeping function called from invalid context at /home/paul/git/linux-rt/kernel/rtmutex.c:659
>>> in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
>>> 2 locks held by swapper/0/0:
>>> #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
>>> #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
>>> irq event stamp: 6121390
>>> hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
>>> hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
>>> softirqs last enabled at (0): [< (null)>] (null)
>>> softirqs last disabled at (0): [< (null)>] (null)
>>> Preemption disabled at:[<ffffffff810ebb9a>] cpu_startup_entry+0x1ba/0x430
>>>
>>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
>>> Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
>>> ffffffff8201c440 ffff880223603cf0 ffffffff819f177d ffff880223603d18
>>> ffffffff810c90d3 ffff880214a50110 0000000000000001 0000000000000001
>>> ffff880223603d38 ffffffff819f89a4 ffff880214a50110 ffff880214a50110
>>> Call Trace:
>>> <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
>>> [<ffffffff810c90d3>] __might_sleep+0x153/0x250
>>> [<ffffffff819f89a4>] rt_spin_lock+0x24/0x60
>>> [<ffffffff810ccdd6>] __wake_up+0x36/0x70
>>> [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
>>
>> -rt lacks an atomic waitqueue for triggering VCPU wakeups on MSIs from
>> assigned devices directly from the host IRQ handler. We need to disable
>> this fast-path in -rt or introduce such an abstraction (I did this once
>> over 2.6.33-rt).
>
> Ah, right -- the simple wait queue support (currently -rt specific)
> would have to be used here. It is on the todo list to get that moved
> from -rt into mainline.
Oh, it's there in -rt already - perfect! If there is a good reason for
upstream, kvm can switch of course.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
On Fri, Sep 20, 2013 at 08:04:19PM +0200, Jan Kiszka wrote:
> On 2013-09-20 19:51, Paul Gortmaker wrote:
> > [Re: [PATCH 0/3] KVM: Make kvm_lock non-raw] On 16/09/2013 (Mon 18:12) Paul Gortmaker wrote:
> >
> >> On 13-09-16 10:06 AM, Paolo Bonzini wrote:
> >>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> >>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> >>> patch that shrunk the kvm_lock critical section so that the mmu_lock
> >>> critical section does not nest with it, but in the end there is no reason
> >>> for the vm_list to be protected by a raw spinlock. Only manipulations
> >>> of kvm_usage_count and the consequent hardware_enable/disable operations
> >>> are not preemptable.
> >>>
> >>> This small series thus splits the kvm_lock in the "raw" part and the
> >>> "non-raw" part.
> >>>
> >>> Paul, could you please provide your Tested-by?
> >>
> >> Sure, I'll go back and see if I can find what triggered it in the
> >> original report, and give the patches a spin on 3.4.x-rt (and probably
> >> 3.10.x-rt, since that is where rt-current is presently).
> >
> > Seems fine on 3.4-rt. On 3.10.10-rt7 it looks like there are other
> > issues, probably not explicitly related to this patchset (see below).
> >
> > Paul.
> > --
> >
> > e1000e 0000:00:19.0 eth1: removed PHC
> > assign device 0:0:19.0
> > pci 0000:00:19.0: irq 43 for MSI/MSI-X
> > pci 0000:00:19.0: irq 43 for MSI/MSI-X
> > pci 0000:00:19.0: irq 43 for MSI/MSI-X
> > pci 0000:00:19.0: irq 43 for MSI/MSI-X
> > BUG: sleeping function called from invalid context at /home/paul/git/linux-rt/kernel/rtmutex.c:659
> > in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
> > 2 locks held by swapper/0/0:
> > #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
> > #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> > irq event stamp: 6121390
> > hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
> > hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
> > softirqs last enabled at (0): [< (null)>] (null)
> > softirqs last disabled at (0): [< (null)>] (null)
> > Preemption disabled at:[<ffffffff810ebb9a>] cpu_startup_entry+0x1ba/0x430
> >
> > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
> > Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
> > ffffffff8201c440 ffff880223603cf0 ffffffff819f177d ffff880223603d18
> > ffffffff810c90d3 ffff880214a50110 0000000000000001 0000000000000001
> > ffff880223603d38 ffffffff819f89a4 ffff880214a50110 ffff880214a50110
> > Call Trace:
> > <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
> > [<ffffffff810c90d3>] __might_sleep+0x153/0x250
> > [<ffffffff819f89a4>] rt_spin_lock+0x24/0x60
> > [<ffffffff810ccdd6>] __wake_up+0x36/0x70
> > [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
>
> -rt lacks an atomic waitqueue for triggering VCPU wakeups on MSIs from
> assigned devices directly from the host IRQ handler. We need to disable
> this fast-path in -rt or introduce such an abstraction (I did this once
> over 2.6.33-rt).
>
> IIRC, VFIO goes the slower patch via a kernel thread unconditionally,
> thus cannot trigger this.
AFAIK VFIO just uses eventfds and these can
inject MSI interrupts directly from IRQ without going through a thread.
> Only legacy device assignment is affected.
>
> Jan
>
> > [<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
> > [<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
> > [<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
> > [<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> > [<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
> > [<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
> > [<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
> > [<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
> > [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> > [<ffffffff8113cec8>] handle_irq_event+0x48/0x70
> > [<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
> > [<ffffffff8104c6ae>] handle_irq+0x1e/0x30
> > [<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
> > [<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
> > <EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
> > [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> > [<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
> > [<ffffffff819db767>] rest_init+0x137/0x140
> > [<ffffffff819db635>] ? rest_init+0x5/0x140
> > [<ffffffff822fde18>] start_kernel+0x3af/0x3bc
> > [<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
> > [<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
> > [<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
> >
> > =================================
> > [ INFO: inconsistent lock state ]
> > 3.10.10-rt7 #2 Not tainted
> > ---------------------------------
> > inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> > swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
> > (&(&(&q->lock)->lock)->wait_lock){?.+.-.}, at: [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
> > {HARDIRQ-ON-W} state was registered at:
> > [<ffffffff810fc94d>] __lock_acquire+0x69d/0x20e0
> > [<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
> > [<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
> > [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
> > [<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
> > [<ffffffff810ccdd6>] __wake_up+0x36/0x70
> > [<ffffffff8109c5ce>] run_timer_softirq+0x1be/0x390
> > [<ffffffff81092a09>] do_current_softirqs+0x239/0x5b0
> > [<ffffffff81092db8>] run_ksoftirqd+0x38/0x60
> > [<ffffffff810c5d7c>] smpboot_thread_fn+0x22c/0x340
> > [<ffffffff810bbf4d>] kthread+0xcd/0xe0
> > [<ffffffff81a019dc>] ret_from_fork+0x7c/0xb0
> > irq event stamp: 6121390
> > hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
> > hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
> > softirqs last enabled at (0): [< (null)>] (null)
> > softirqs last disabled at (0): [< (null)>] (null)
> >
> > other info that might help us debug this:
> > Possible unsafe locking scenario:
> >
> > CPU0
> > ----
> > lock(&(&(&q->lock)->lock)->wait_lock);
> > <Interrupt>
> > lock(&(&(&q->lock)->lock)->wait_lock);
> >
> > *** DEADLOCK ***
> >
> > 2 locks held by swapper/0/0:
> > #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
> > #1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> >
> > stack backtrace:
> > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
> > Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
> > ffffffff8262b550 ffff880223603a40 ffffffff819f177d ffff880223603a90
> > ffffffff819ec532 0000000000000000 ffffffff00000000 ffff880200000001
> > 0000000000000002 ffffffff8201ccc0 ffffffff810f9040 0000000000000000
> > Call Trace:
> > <IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
> > [<ffffffff819ec532>] print_usage_bug.part.36+0x28b/0x29a
> > [<ffffffff810f9040>] ? check_usage_backwards+0x150/0x150
> > [<ffffffff810f9dab>] mark_lock+0x28b/0x6a0
> > [<ffffffff810fcbf9>] __lock_acquire+0x949/0x20e0
> > [<ffffffff811091f2>] ? __module_text_address+0x12/0x60
> > [<ffffffff8110ea8f>] ? is_module_text_address+0x2f/0x60
> > [<ffffffff810b8408>] ? __kernel_text_address+0x58/0x80
> > [<ffffffff8104dbb2>] ? print_context_stack+0x62/0xf0
> > [<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
> > [<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
> > [<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
> > [<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
> > [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
> > [<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
> > [<ffffffff810ccdd6>] __wake_up+0x36/0x70
> > [<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
> > [<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
> > [<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
> > [<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
> > [<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
> > [<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
> > [<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
> > [<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
> > [<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
> > [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> > [<ffffffff8113cec8>] handle_irq_event+0x48/0x70
> > [<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
> > [<ffffffff8104c6ae>] handle_irq+0x1e/0x30
> > [<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
> > [<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
> > <EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
> > [<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
> > [<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
> > [<ffffffff819db767>] rest_init+0x137/0x140
> > [<ffffffff819db635>] ? rest_init+0x5/0x140
> > [<ffffffff822fde18>] start_kernel+0x3af/0x3bc
> > [<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
> > [<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
> > [<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf
>
> --
> Siemens AG, Corporate Technology, CT RTC ITP SES-DE
> Corporate Competence Center Embedded Linux
On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote:
> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> patch that shrunk the kvm_lock critical section so that the mmu_lock
> critical section does not nest with it, but in the end there is no reason
> for the vm_list to be protected by a raw spinlock. Only manipulations
> of kvm_usage_count and the consequent hardware_enable/disable operations
> are not preemptable.
>
> This small series thus splits the kvm_lock in the "raw" part and the
> "non-raw" part.
>
> Paul, could you please provide your Tested-by?
>
Reviewed-by: Gleb Natapov <[email protected]>
But why should it go to stable?
> Thanks,
>
> Paolo
>
> Paolo Bonzini (3):
> KVM: cleanup (physical) CPU hotplug
> KVM: protect kvm_usage_count with its own spinlock
> KVM: Convert kvm_lock back to non-raw spinlock
>
> Documentation/virtual/kvm/locking.txt | 8 ++++--
> arch/x86/kvm/mmu.c | 4 +--
> arch/x86/kvm/x86.c | 8 +++---
> include/linux/kvm_host.h | 2 +-
> virt/kvm/kvm_main.c | 51 ++++++++++++++++++-----------------
> 5 files changed, 40 insertions(+), 33 deletions(-)
>
> --
> 1.8.3.1
--
Gleb.
Il 22/09/2013 09:42, Gleb Natapov ha scritto:
> On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote:
>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
>> patch that shrunk the kvm_lock critical section so that the mmu_lock
>> critical section does not nest with it, but in the end there is no reason
>> for the vm_list to be protected by a raw spinlock. Only manipulations
>> of kvm_usage_count and the consequent hardware_enable/disable operations
>> are not preemptable.
>>
>> This small series thus splits the kvm_lock in the "raw" part and the
>> "non-raw" part.
>>
>> Paul, could you please provide your Tested-by?
>>
> Reviewed-by: Gleb Natapov <[email protected]>
>
> But why should it go to stable?
It is a regression from before the kvm_lock was made raw. Secondarily,
it takes a much longer time before a patch hits -rt trees (can even be
as much as a year) and this patch does nothing on non-rt trees. So
without putting it into stable it would get no actual coverage.
Paolo
On Sun, Sep 22, 2013 at 10:53:14AM +0200, Paolo Bonzini wrote:
> Il 22/09/2013 09:42, Gleb Natapov ha scritto:
> > On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote:
> >> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> >> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> >> patch that shrunk the kvm_lock critical section so that the mmu_lock
> >> critical section does not nest with it, but in the end there is no reason
> >> for the vm_list to be protected by a raw spinlock. Only manipulations
> >> of kvm_usage_count and the consequent hardware_enable/disable operations
> >> are not preemptable.
> >>
> >> This small series thus splits the kvm_lock in the "raw" part and the
> >> "non-raw" part.
> >>
> >> Paul, could you please provide your Tested-by?
> >>
> > Reviewed-by: Gleb Natapov <[email protected]>
> >
> > But why should it go to stable?
>
> It is a regression from before the kvm_lock was made raw. Secondarily,
It was made raw in 2.6.39 and commit message claims that it is done for
-rt sake, why regression was noticed only now?
> it takes a much longer time before a patch hits -rt trees (can even be
> as much as a year) and this patch does nothing on non-rt trees. So
> without putting it into stable it would get no actual coverage.
>
The change is not completely trivial, it splits lock. There is no
obvious problem of course, otherwise you wouldn't send it and I
would ack it :), but it does not mean that the chance for problem is
zero, so why risk stability of stable even a little bit if the patch
does not fix anything in stable?
I do not know how -rt development goes and how it affects decisions for
stable acceptance, why can't they carry the patch in their tree until
they move to 3.12?
--
Gleb.
On 2013-09-22 11:53, Gleb Natapov wrote:
> On Sun, Sep 22, 2013 at 10:53:14AM +0200, Paolo Bonzini wrote:
>> Il 22/09/2013 09:42, Gleb Natapov ha scritto:
>>> On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote:
>>>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
>>>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
>>>> patch that shrunk the kvm_lock critical section so that the mmu_lock
>>>> critical section does not nest with it, but in the end there is no reason
>>>> for the vm_list to be protected by a raw spinlock. Only manipulations
>>>> of kvm_usage_count and the consequent hardware_enable/disable operations
>>>> are not preemptable.
>>>>
>>>> This small series thus splits the kvm_lock in the "raw" part and the
>>>> "non-raw" part.
>>>>
>>>> Paul, could you please provide your Tested-by?
>>>>
>>> Reviewed-by: Gleb Natapov <[email protected]>
>>>
>>> But why should it go to stable?
>>
>> It is a regression from before the kvm_lock was made raw. Secondarily,
> It was made raw in 2.6.39 and commit message claims that it is done for
> -rt sake, why regression was noticed only now?
Probably, the patch is stressed to infrequently. Just checked: the issue
was present from day #1 one, what a shame.
>
>> it takes a much longer time before a patch hits -rt trees (can even be
>> as much as a year) and this patch does nothing on non-rt trees. So
>> without putting it into stable it would get no actual coverage.
>>
> The change is not completely trivial, it splits lock. There is no
> obvious problem of course, otherwise you wouldn't send it and I
> would ack it :), but it does not mean that the chance for problem is
> zero, so why risk stability of stable even a little bit if the patch
> does not fix anything in stable?
>
> I do not know how -rt development goes and how it affects decisions for
> stable acceptance, why can't they carry the patch in their tree until
> they move to 3.12?
I think it would be fair to let stable -rt carry these. -rt requires
more specific patching anyway due to the waitqueue issue Paul reported.
But CC'ing Steven to obtain his view.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
On 13-09-22 05:53 AM, Gleb Natapov wrote:
> On Sun, Sep 22, 2013 at 10:53:14AM +0200, Paolo Bonzini wrote:
>> Il 22/09/2013 09:42, Gleb Natapov ha scritto:
>>> On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote:
>>>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
>>>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
>>>> patch that shrunk the kvm_lock critical section so that the mmu_lock
>>>> critical section does not nest with it, but in the end there is no reason
>>>> for the vm_list to be protected by a raw spinlock. Only manipulations
>>>> of kvm_usage_count and the consequent hardware_enable/disable operations
>>>> are not preemptable.
>>>>
>>>> This small series thus splits the kvm_lock in the "raw" part and the
>>>> "non-raw" part.
>>>>
>>>> Paul, could you please provide your Tested-by?
>>>>
>>> Reviewed-by: Gleb Natapov <[email protected]>
>>>
>>> But why should it go to stable?
>>
>> It is a regression from before the kvm_lock was made raw. Secondarily,
> It was made raw in 2.6.39 and commit message claims that it is done for
> -rt sake, why regression was noticed only now?
>
>> it takes a much longer time before a patch hits -rt trees (can even be
>> as much as a year) and this patch does nothing on non-rt trees. So
>> without putting it into stable it would get no actual coverage.
>>
> The change is not completely trivial, it splits lock. There is no
> obvious problem of course, otherwise you wouldn't send it and I
> would ack it :), but it does not mean that the chance for problem is
> zero, so why risk stability of stable even a little bit if the patch
> does not fix anything in stable?
>
> I do not know how -rt development goes and how it affects decisions for
> stable acceptance, why can't they carry the patch in their tree until
> they move to 3.12?
The -rt tree regularly carries mainline backports that are of interest
to -rt but perhaps not of interest to stable, so there is no problem
doing the same with content like this, if desired.
Thanks,
Paul.
--
>
> --
> Gleb.
>
Il 23/09/2013 15:36, Paul Gortmaker ha scritto:
>> > The change is not completely trivial, it splits lock. There is no
>> > obvious problem of course, otherwise you wouldn't send it and I
>> > would ack it :), but it does not mean that the chance for problem is
>> > zero, so why risk stability of stable even a little bit if the patch
>> > does not fix anything in stable?
>> >
>> > I do not know how -rt development goes and how it affects decisions for
>> > stable acceptance, why can't they carry the patch in their tree until
>> > they move to 3.12?
> The -rt tree regularly carries mainline backports that are of interest
> to -rt but perhaps not of interest to stable, so there is no problem
> doing the same with content like this, if desired.
Perfect, I'll queue [v2 of] these patches for 3.12 then.
Paolo
On Mon, Sep 23, 2013 at 03:44:21PM +0200, Paolo Bonzini wrote:
> Il 23/09/2013 15:36, Paul Gortmaker ha scritto:
> >> > The change is not completely trivial, it splits lock. There is no
> >> > obvious problem of course, otherwise you wouldn't send it and I
> >> > would ack it :), but it does not mean that the chance for problem is
> >> > zero, so why risk stability of stable even a little bit if the patch
> >> > does not fix anything in stable?
> >> >
> >> > I do not know how -rt development goes and how it affects decisions for
> >> > stable acceptance, why can't they carry the patch in their tree until
> >> > they move to 3.12?
> > The -rt tree regularly carries mainline backports that are of interest
> > to -rt but perhaps not of interest to stable, so there is no problem
> > doing the same with content like this, if desired.
>
> Perfect, I'll queue [v2 of] these patches for 3.12 then.
>
Why 3.12 if it is not going to stable?
--
Gleb.
Il 23/09/2013 16:59, Gleb Natapov ha scritto:
> > Perfect, I'll queue [v2 of] these patches for 3.12 then.
>
> Why 3.12 if it is not going to stable?
Off-by-one. :)
Paolo