Hi,
Series is fixed to address Linus and Ben comments:
* Turn __ARCH_IRQ_EXIT_ON_IRQ_STACK old ad-hoc style symbol to proper Kconfig
(CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK)
* Activates it to powerpc as well.
* Fix a bit the changelog of patch 6/8
This applies on top of 06367d58f487a592de50e6e2327371c5e3b6188f
("Merge branch 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc")
And it can be pulled from:
git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
irq/core-v4
HEAD: 0362b2ff8d67913a8ffc5d757500129ead56b007
Frederic Weisbecker (8):
irq: Force hardirq exit's softirq processing on its own stack
irq: Consolidate do_softirq() arch overriden implementations
irq: Optimize call to softirq on hardirq exit
irq: Improve a bit softirq debugging
irq: Justify the various softirq stack choices
irq: Optimize softirq stack selection in irq exit
x86: Tell about irq stack coverage
powerpc: Tell about irq stack coverage
arch/Kconfig | 10 ++++++++
arch/metag/kernel/irq.c | 52 ++++++++++++++++--------------------------
arch/parisc/kernel/irq.c | 17 ++------------
arch/powerpc/Kconfig | 1 +
arch/powerpc/kernel/irq.c | 17 +-------------
arch/s390/kernel/irq.c | 52 +++++++++++++++++-------------------------
arch/sh/kernel/irq.c | 57 +++++++++++++++++-----------------------------
arch/sparc/kernel/irq_64.c | 31 ++++++++-----------------
arch/x86/Kconfig | 1 +
arch/x86/kernel/entry_64.S | 4 ++--
arch/x86/kernel/irq_32.c | 30 +++++++-----------------
arch/x86/kernel/irq_64.c | 21 -----------------
include/linux/interrupt.h | 11 +++++++++
kernel/softirq.c | 40 ++++++++++++++++++++++++--------
14 files changed, 138 insertions(+), 206 deletions(-)
--
1.8.3.1
The commit facd8b80c67a3cf64a467c4a2ac5fb31f2e6745b
("irq: Sanitize invoke_softirq") converted irq exit
calls of do_softirq() to __do_softirq() on all architectures,
assuming it was only used there for its irq disablement
properties.
But as a side effect, the softirqs processed in the end
of the hardirq are always called on the inline current
stack that is used by irq_exit() instead of the softirq
stack provided by the archs that override do_softirq().
The result is mostly safe if the architecture runs irq_exit()
on a separate irq stack because then softirqs are processed
on that same stack that is near empty at this stage (assuming
hardirq aren't nesting).
Otherwise irq_exit() runs in the task stack and so does the softirq
too. The interrupted call stack can be randomly deep already and
the softirq can dig through it even further. To add insult to the
injury, this softirq can be interrupted by a new hardirq, maximizing
the chances for a stack overrun as reported in powerpc for example:
[ 1002.364577] do_IRQ: stack overflow: 1920
[ 1002.364653] CPU: 0 PID: 1602 Comm: qemu-system-ppc Not tainted 3.10.4-300.1.fc19.ppc64p7 #1
[ 1002.364734] Call Trace:
[ 1002.364770] [c0000000050a8740] [c0000000000157c0] .show_stack+0x130/0x200 (unreliable)
[ 1002.364872] [c0000000050a8810] [c00000000082f6d0] .dump_stack+0x28/0x3c
[ 1002.364955] [c0000000050a8880] [c000000000010b98] .do_IRQ+0x2b8/0x2c0
[ 1002.365039] [c0000000050a8930] [c0000000000026d4] hardware_interrupt_common+0x154/0x180
[ 1002.365148] --- Exception: 501 at .cp_start_xmit+0x3a4/0x820 [8139cp]
[ 1002.365148] LR = .cp_start_xmit+0x390/0x820 [8139cp]
[ 1002.365359] [c0000000050a8d40] [c0000000006d7f14] .dev_hard_start_xmit+0x394/0x640
[ 1002.365433] [c0000000050a8e00] [c0000000007028c0] .sch_direct_xmit+0x110/0x260
[ 1002.365499] [c0000000050a8ea0] [c0000000006d8420] .dev_queue_xmit+0x260/0x630
[ 1002.365571] [c0000000050a8f40] [d0000000027d30d4] .br_dev_queue_push_xmit+0xc4/0x130 [bridge]
[ 1002.365641] [c0000000050a8fc0] [d0000000027d01f8] .br_dev_xmit+0x198/0x270 [bridge]
[ 1002.365707] [c0000000050a9070] [c0000000006d7f14] .dev_hard_start_xmit+0x394/0x640
[ 1002.365774] [c0000000050a9130] [c0000000006d85e8] .dev_queue_xmit+0x428/0x630
[ 1002.365834] [c0000000050a91d0] [c000000000729764] .ip_finish_output+0x2a4/0x550
[ 1002.365902] [c0000000050a9290] [c00000000072aaf0] .ip_local_out+0x50/0x70
[ 1002.365960] [c0000000050a9310] [c00000000072aed8] .ip_queue_xmit+0x148/0x420
[ 1002.366018] [c0000000050a93b0] [c000000000749524] .tcp_transmit_skb+0x4e4/0xaf0
[ 1002.366085] [c0000000050a94a0] [c00000000073de9c] .__tcp_ack_snd_check+0x7c/0xf0
[ 1002.366152] [c0000000050a9520] [c0000000007451d8] .tcp_rcv_established+0x1e8/0x930
[ 1002.366217] [c0000000050a95f0] [c00000000075326c] .tcp_v4_do_rcv+0x21c/0x570
[ 1002.366274] [c0000000050a96c0] [c000000000754a44] .tcp_v4_rcv+0x734/0x930
[ 1002.366332] [c0000000050a97a0] [c000000000724144] .ip_local_deliver_finish+0x184/0x360
[ 1002.366398] [c0000000050a9840] [c000000000724468] .ip_rcv_finish+0x148/0x400
[ 1002.366457] [c0000000050a98d0] [c0000000006d3248] .__netif_receive_skb_core+0x4f8/0xb00
[ 1002.366523] [c0000000050a99d0] [c0000000006d5414] .netif_receive_skb+0x44/0x110
[ 1002.366594] [c0000000050a9a70] [d0000000027d4e2c] .br_handle_frame_finish+0x2bc/0x3f0 [bridge]
[ 1002.366674] [c0000000050a9b20] [d0000000027de5ac] .br_nf_pre_routing_finish+0x2ac/0x420 [bridge]
[ 1002.366754] [c0000000050a9bd0] [d0000000027df5ec] .br_nf_pre_routing+0x4dc/0x7d0 [bridge]
[ 1002.366820] [c0000000050a9c70] [c000000000717aa4] .nf_iterate+0x114/0x130
[ 1002.366877] [c0000000050a9d30] [c000000000717b74] .nf_hook_slow+0xb4/0x1e0
[ 1002.366938] [c0000000050a9e00] [d0000000027d51f0] .br_handle_frame+0x290/0x330 [bridge]
[ 1002.367005] [c0000000050a9ea0] [c0000000006d309c] .__netif_receive_skb_core+0x34c/0xb00
[ 1002.367072] [c0000000050a9fa0] [c0000000006d5414] .netif_receive_skb+0x44/0x110
[ 1002.367138] [c0000000050aa040] [c0000000006d6218] .napi_gro_receive+0xe8/0x120
[ 1002.367210] [c0000000050aa0c0] [d00000000208536c] .cp_rx_poll+0x31c/0x590 [8139cp]
[ 1002.367276] [c0000000050aa1d0] [c0000000006d59cc] .net_rx_action+0x1dc/0x310
[ 1002.367335] [c0000000050aa2b0] [c0000000000a0568] .__do_softirq+0x158/0x330
[ 1002.367394] [c0000000050aa3b0] [c0000000000a0978] .irq_exit+0xc8/0x110
[ 1002.367452] [c0000000050aa430] [c0000000000109bc] .do_IRQ+0xdc/0x2c0
[ 1002.367510] [c0000000050aa4e0] [c0000000000026d4] hardware_interrupt_common+0x154/0x180
[ 1002.367580] --- Exception: 501 at .bad_range+0x1c/0x110
[ 1002.367580] LR = .get_page_from_freelist+0x908/0xbb0
[ 1002.367658] [c0000000050aa7d0] [c00000000041d758] .list_del+0x18/0x50 (unreliable)
[ 1002.367725] [c0000000050aa850] [c0000000001bfa98] .get_page_from_freelist+0x908/0xbb0
[ 1002.367792] [c0000000050aa9e0] [c0000000001bff5c] .__alloc_pages_nodemask+0x21c/0xae0
[ 1002.367860] [c0000000050aaba0] [c0000000002126d0] .alloc_pages_vma+0xd0/0x210
[ 1002.367918] [c0000000050aac60] [c0000000001e93f4] .handle_pte_fault+0x814/0xb70
[ 1002.367985] [c0000000050aad50] [c0000000001eade4] .__get_user_pages+0x1a4/0x640
[ 1002.368052] [c0000000050aae60] [c00000000004606c] .get_user_pages_fast+0xec/0x160
[ 1002.368130] [c0000000050aaf10] [d000000001f73930] .__gfn_to_pfn_memslot+0x3b0/0x430 [kvm]
[ 1002.368205] [c0000000050aafd0] [d000000001f7e214] .kvmppc_gfn_to_pfn+0x64/0x130 [kvm]
[ 1002.368280] [c0000000050ab070] [d000000001f8a824] .kvmppc_mmu_map_page+0x94/0x530 [kvm]
[ 1002.368354] [c0000000050ab190] [d000000001f85064] .kvmppc_handle_pagefault+0x174/0x610 [kvm]
[ 1002.368429] [c0000000050ab270] [d000000001f85b74] .kvmppc_handle_exit_pr+0x464/0x9b0 [kvm]
[ 1002.368504] [c0000000050ab320] [d000000001f88ec4] kvm_start_lightweight+0x1ec/0x1fc [kvm]
[ 1002.368578] [c0000000050ab4f0] [d000000001f86a58] .kvmppc_vcpu_run_pr+0x168/0x3b0 [kvm]
[ 1002.368652] [c0000000050ab9c0] [d000000001f7f218] .kvmppc_vcpu_run+0xc8/0xf0 [kvm]
[ 1002.368725] [c0000000050aba50] [d000000001f7bdac] .kvm_arch_vcpu_ioctl_run+0x5c/0x1a0 [kvm]
[ 1002.368797] [c0000000050abae0] [d000000001f74618] .kvm_vcpu_ioctl+0x478/0x730 [kvm]
[ 1002.368865] [c0000000050abc90] [c00000000025302c] .do_vfs_ioctl+0x4ec/0x7c0
[ 1002.368923] [c0000000050abd80] [c0000000002533d4] .SyS_ioctl+0xd4/0xf0
[ 1002.368981] [c0000000050abe30] [c000000000009ed4] syscall_exit+0x0/0x98
Since this is a regression, this patch proposes a minimalistic
and low-risk solution by blindly forcing the hardirq exit processing of
softirqs on the softirq stack. This way we should reduce significantly
the opportunities for task stack overflow dug by softirqs.
Longer term solutions may involve extending the hardirq stack coverage to
irq_exit(), etc...
Reported-by: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
kernel/softirq.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 53cc09c..d7d498d 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -328,10 +328,19 @@ void irq_enter(void)
static inline void invoke_softirq(void)
{
- if (!force_irqthreads)
- __do_softirq();
- else
+ if (!force_irqthreads) {
+ /*
+ * We can safely execute softirq on the current stack if
+ * it is the irq stack, because it should be near empty
+ * at this stage. But we have no way to know if the arch
+ * calls irq_exit() on the irq stack. So call softirq
+ * in its own stack to prevent from any overrun on top
+ * of a potentially deep task stack.
+ */
+ do_softirq();
+ } else {
wakeup_softirqd();
+ }
}
static inline void tick_irq_exit(void)
--
1.8.3.1
do_softirq() has a debug check that verifies that it is not nesting
on softirqs processing, nor miscounting the softirq part of the preempt
count.
But making sure that softirqs processing don't nest is actually a more
generic concern that applies to any caller of __do_softirq().
Do take it one step further and generalize that debug check to
any softirq processing.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
kernel/softirq.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 17c5cd2..9f8092b 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -133,7 +133,6 @@ EXPORT_SYMBOL(local_bh_disable);
static void __local_bh_enable(unsigned int cnt)
{
- WARN_ON_ONCE(in_irq());
WARN_ON_ONCE(!irqs_disabled());
if (softirq_count() == cnt)
@@ -148,6 +147,7 @@ static void __local_bh_enable(unsigned int cnt)
*/
void _local_bh_enable(void)
{
+ WARN_ON_ONCE(in_irq());
__local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
}
@@ -279,6 +279,7 @@ restart:
account_irq_exit_time(current);
__local_bh_enable(SOFTIRQ_OFFSET);
+ WARN_ON_ONCE(in_interrupt());
tsk_restore_flags(current, old_flags, PF_MEMALLOC);
}
@@ -299,7 +300,6 @@ asmlinkage void do_softirq(void)
if (pending)
do_softirq_own_stack();
- WARN_ON_ONCE(softirq_count());
local_irq_restore(flags);
}
--
1.8.3.1
If irq_exit() is called on the arch's specified irq stack,
it should be safe to run softirqs inline under that same
irq stack as it is near empty by the time we call irq_exit().
For example if we use the same stack for both hard and soft irqs here,
the worst case scenario is:
hardirq -> softirq -> hardirq. But then the softirq supersedes the
first hardirq as the stack user since irq_exit() is called in
a mostly empty stack. So the stack merge in this case looks acceptable.
Stack overrun still have a chance to happen if hardirqs have more
opportunities to nest, but then it's another problem to solve.
So lets adapt the irq exit's softirq stack on top of a new Kconfig symbol
that can be defined when irq_exit() runs on the irq stack. That way
we can spare some stack switch on irq processing and all the cache
issues that come along.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
arch/Kconfig | 10 ++++++++++
kernel/softirq.c | 14 ++++++++++----
2 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 1feb169..5293e8a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -393,6 +393,16 @@ config HAVE_UNDERSCORE_SYMBOL_PREFIX
Some architectures generate an _ in front of C symbols; things like
module loading and assembly files need to know about this.
+config HAVE_IRQ_EXIT_ON_IRQ_STACK
+ bool
+ help
+ Architecture doesn't only execute the irq handler on the irq stack
+ but also irq_exit(). This way we can process softirqs on this irq
+ stack instead of switching to a new one when we call __do_softirq()
+ in the end of an hardirq.
+ This spares a stack switch and improves cache usage on softirq
+ processing.
+
#
# ABI hall of shame
#
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 2b4328e..dacd0ab 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -332,15 +332,21 @@ void irq_enter(void)
static inline void invoke_softirq(void)
{
if (!force_irqthreads) {
+#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
/*
* We can safely execute softirq on the current stack if
* it is the irq stack, because it should be near empty
- * at this stage. But we have no way to know if the arch
- * calls irq_exit() on the irq stack. So call softirq
- * in its own stack to prevent from any overrun on top
- * of a potentially deep task stack.
+ * at this stage.
+ */
+ __do_softirq();
+#else
+ /*
+ * Otherwise, irq_exit() is called on the task stack that can
+ * be potentially deep already. So call softirq in its own stack
+ * to prevent from any overrun.
*/
do_softirq_own_stack();
+#endif
} else {
wakeup_softirqd();
}
--
1.8.3.1
Now that powerpc runs irq_exit() under the irq stack,
let the softirq core know about that so that we spare
the needless stack switch on irq exit's softirq processing.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
arch/powerpc/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 38f3b7e..b365d5c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -138,6 +138,7 @@ config PPC
select OLD_SIGSUSPEND
select OLD_SIGACTION if PPC32
select HAVE_DEBUG_STACKOVERFLOW
+ select HAVE_IRQ_EXIT_ON_IRQ_STACK
config EARLY_PRINTK
bool
--
1.8.3.1
For clarity, comment the various stack choices for softirqs
processing, whether we execute them from ksoftirqd or
local_irq_enable() calls.
Their use on irq_exit() is already commented.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
kernel/softirq.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 9f8092b..2b4328e 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -170,8 +170,13 @@ static inline void _local_bh_enable_ip(unsigned long ip)
*/
sub_preempt_count(SOFTIRQ_DISABLE_OFFSET - 1);
- if (unlikely(!in_interrupt() && local_softirq_pending()))
+ if (unlikely(!in_interrupt() && local_softirq_pending())) {
+ /*
+ * Run softirq if any pending. And do it in its own stack
+ * as we may be calling this deep in a task call stack already.
+ */
do_softirq();
+ }
dec_preempt_count();
#ifdef CONFIG_TRACE_IRQFLAGS
@@ -769,6 +774,10 @@ static void run_ksoftirqd(unsigned int cpu)
{
local_irq_disable();
if (local_softirq_pending()) {
+ /*
+ * We can safely run softirq on inline stack, as we are not deep
+ * in the task stack here.
+ */
__do_softirq();
rcu_note_context_switch(cpu);
local_irq_enable();
--
1.8.3.1
x86-64 runs irq_exit() under the irq stack. So it can afford
to run softirqs in hardirq exit without the need to switch
the stacks. The hardirq stack is good enough for that.
Now x86-64 runs softirqs in the hardirq stack anyway, so what we
mostly skip is some needless per cpu refcounting updates there.
x86-32 is not concerned because it only runs the irq handler on
the irq stack.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
arch/x86/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ee2fb9d..99eb1cc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -123,6 +123,7 @@ config X86
select COMPAT_OLD_SIGACTION if IA32_EMULATION
select RTC_LIB
select HAVE_DEBUG_STACKOVERFLOW
+ select HAVE_IRQ_EXIT_ON_IRQ_STACK if X86_64
config INSTRUCTION_DECODER
def_bool y
--
1.8.3.1
Before processing softirqs on hardirq exit, we already
do the check for pending softirqs while hardirqs are
guaranteed to be disabled.
So we can take a shortcut and safely jump to the arch
specific implementation directly.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
kernel/softirq.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 26ee727..17c5cd2 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -335,7 +335,7 @@ static inline void invoke_softirq(void)
* in its own stack to prevent from any overrun on top
* of a potentially deep task stack.
*/
- do_softirq();
+ do_softirq_own_stack();
} else {
wakeup_softirqd();
}
--
1.8.3.1
All arch overriden implementations of do_softirq() share the following
common code: disable irqs (to avoid races with the pending check),
check if there are softirqs pending, then execute __do_softirq() on
a specific stack.
Consolidate the common parts such that archs only worry about the
stack switch.
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Andrew Morton <[email protected]>
---
arch/metag/kernel/irq.c | 52 ++++++++++++++++--------------------------
arch/parisc/kernel/irq.c | 17 ++------------
arch/powerpc/kernel/irq.c | 17 +-------------
arch/s390/kernel/irq.c | 52 +++++++++++++++++-------------------------
arch/sh/kernel/irq.c | 57 +++++++++++++++++-----------------------------
arch/sparc/kernel/irq_64.c | 31 ++++++++-----------------
arch/x86/kernel/entry_64.S | 4 ++--
arch/x86/kernel/irq_32.c | 30 +++++++-----------------
arch/x86/kernel/irq_64.c | 21 -----------------
include/linux/interrupt.h | 11 +++++++++
kernel/softirq.c | 8 +++----
11 files changed, 98 insertions(+), 202 deletions(-)
diff --git a/arch/metag/kernel/irq.c b/arch/metag/kernel/irq.c
index 2a2c9d5..3b4b7f6 100644
--- a/arch/metag/kernel/irq.c
+++ b/arch/metag/kernel/irq.c
@@ -159,44 +159,30 @@ void irq_ctx_exit(int cpu)
extern asmlinkage void __do_softirq(void);
-asmlinkage void do_softirq(void)
+void do_softirq_own_stack(void)
{
- unsigned long flags;
struct thread_info *curctx;
union irq_ctx *irqctx;
u32 *isp;
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
-
- if (local_softirq_pending()) {
- curctx = current_thread_info();
- irqctx = softirq_ctx[smp_processor_id()];
- irqctx->tinfo.task = curctx->task;
-
- /* build the stack frame on the softirq stack */
- isp = (u32 *) ((char *)irqctx + sizeof(struct thread_info));
-
- asm volatile (
- "MOV D0.5,%0\n"
- "SWAP A0StP,D0.5\n"
- "CALLR D1RtP,___do_softirq\n"
- "MOV A0StP,D0.5\n"
- :
- : "r" (isp)
- : "memory", "cc", "D1Ar1", "D0Ar2", "D1Ar3", "D0Ar4",
- "D1Ar5", "D0Ar6", "D0Re0", "D1Re0", "D0.4", "D1RtP",
- "D0.5"
- );
- /*
- * Shouldn't happen, we returned above if in_interrupt():
- */
- WARN_ON_ONCE(softirq_count());
- }
-
- local_irq_restore(flags);
+ curctx = current_thread_info();
+ irqctx = softirq_ctx[smp_processor_id()];
+ irqctx->tinfo.task = curctx->task;
+
+ /* build the stack frame on the softirq stack */
+ isp = (u32 *) ((char *)irqctx + sizeof(struct thread_info));
+
+ asm volatile (
+ "MOV D0.5,%0\n"
+ "SWAP A0StP,D0.5\n"
+ "CALLR D1RtP,___do_softirq\n"
+ "MOV A0StP,D0.5\n"
+ :
+ : "r" (isp)
+ : "memory", "cc", "D1Ar1", "D0Ar2", "D1Ar3", "D0Ar4",
+ "D1Ar5", "D0Ar6", "D0Re0", "D1Re0", "D0.4", "D1RtP",
+ "D0.5"
+ );
}
#endif
diff --git a/arch/parisc/kernel/irq.c b/arch/parisc/kernel/irq.c
index 2e6443b..ef59276 100644
--- a/arch/parisc/kernel/irq.c
+++ b/arch/parisc/kernel/irq.c
@@ -499,22 +499,9 @@ static void execute_on_irq_stack(void *func, unsigned long param1)
*irq_stack_in_use = 1;
}
-asmlinkage void do_softirq(void)
+void do_softirq_own_stack(void)
{
- __u32 pending;
- unsigned long flags;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
-
- pending = local_softirq_pending();
-
- if (pending)
- execute_on_irq_stack(__do_softirq, 0);
-
- local_irq_restore(flags);
+ execute_on_irq_stack(__do_softirq, 0);
}
#endif /* CONFIG_IRQSTACKS */
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 57d286a..5c4adfc 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -593,7 +593,7 @@ void irq_ctx_init(void)
}
}
-static inline void do_softirq_onstack(void)
+void do_softirq_own_stack(void)
{
struct thread_info *curtp, *irqtp;
@@ -611,21 +611,6 @@ static inline void do_softirq_onstack(void)
set_bits(irqtp->flags, &curtp->flags);
}
-void do_softirq(void)
-{
- unsigned long flags;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
-
- if (local_softirq_pending())
- do_softirq_onstack();
-
- local_irq_restore(flags);
-}
-
irq_hw_number_t virq_to_hw(unsigned int virq)
{
struct irq_data *irq_data = irq_get_irq_data(virq);
diff --git a/arch/s390/kernel/irq.c b/arch/s390/kernel/irq.c
index 8ac2097..bb27a26 100644
--- a/arch/s390/kernel/irq.c
+++ b/arch/s390/kernel/irq.c
@@ -157,39 +157,29 @@ int arch_show_interrupts(struct seq_file *p, int prec)
/*
* Switch to the asynchronous interrupt stack for softirq execution.
*/
-asmlinkage void do_softirq(void)
+void do_softirq_own_stack(void)
{
- unsigned long flags, old, new;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
-
- if (local_softirq_pending()) {
- /* Get current stack pointer. */
- asm volatile("la %0,0(15)" : "=a" (old));
- /* Check against async. stack address range. */
- new = S390_lowcore.async_stack;
- if (((new - old) >> (PAGE_SHIFT + THREAD_ORDER)) != 0) {
- /* Need to switch to the async. stack. */
- new -= STACK_FRAME_OVERHEAD;
- ((struct stack_frame *) new)->back_chain = old;
-
- asm volatile(" la 15,0(%0)\n"
- " basr 14,%2\n"
- " la 15,0(%1)\n"
- : : "a" (new), "a" (old),
- "a" (__do_softirq)
- : "0", "1", "2", "3", "4", "5", "14",
- "cc", "memory" );
- } else {
- /* We are already on the async stack. */
- __do_softirq();
- }
+ unsigned long old, new;
+
+ /* Get current stack pointer. */
+ asm volatile("la %0,0(15)" : "=a" (old));
+ /* Check against async. stack address range. */
+ new = S390_lowcore.async_stack;
+ if (((new - old) >> (PAGE_SHIFT + THREAD_ORDER)) != 0) {
+ /* Need to switch to the async. stack. */
+ new -= STACK_FRAME_OVERHEAD;
+ ((struct stack_frame *) new)->back_chain = old;
+ asm volatile(" la 15,0(%0)\n"
+ " basr 14,%2\n"
+ " la 15,0(%1)\n"
+ : : "a" (new), "a" (old),
+ "a" (__do_softirq)
+ : "0", "1", "2", "3", "4", "5", "14",
+ "cc", "memory" );
+ } else {
+ /* We are already on the async stack. */
+ __do_softirq();
}
-
- local_irq_restore(flags);
}
/*
diff --git a/arch/sh/kernel/irq.c b/arch/sh/kernel/irq.c
index 063af10..0833736 100644
--- a/arch/sh/kernel/irq.c
+++ b/arch/sh/kernel/irq.c
@@ -149,47 +149,32 @@ void irq_ctx_exit(int cpu)
hardirq_ctx[cpu] = NULL;
}
-asmlinkage void do_softirq(void)
+void do_softirq_own_stack(void)
{
- unsigned long flags;
struct thread_info *curctx;
union irq_ctx *irqctx;
u32 *isp;
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
-
- if (local_softirq_pending()) {
- curctx = current_thread_info();
- irqctx = softirq_ctx[smp_processor_id()];
- irqctx->tinfo.task = curctx->task;
- irqctx->tinfo.previous_sp = current_stack_pointer;
-
- /* build the stack frame on the softirq stack */
- isp = (u32 *)((char *)irqctx + sizeof(*irqctx));
-
- __asm__ __volatile__ (
- "mov r15, r9 \n"
- "jsr @%0 \n"
- /* switch to the softirq stack */
- " mov %1, r15 \n"
- /* restore the thread stack */
- "mov r9, r15 \n"
- : /* no outputs */
- : "r" (__do_softirq), "r" (isp)
- : "memory", "r0", "r1", "r2", "r3", "r4",
- "r5", "r6", "r7", "r8", "r9", "r15", "t", "pr"
- );
-
- /*
- * Shouldn't happen, we returned above if in_interrupt():
- */
- WARN_ON_ONCE(softirq_count());
- }
-
- local_irq_restore(flags);
+ curctx = current_thread_info();
+ irqctx = softirq_ctx[smp_processor_id()];
+ irqctx->tinfo.task = curctx->task;
+ irqctx->tinfo.previous_sp = current_stack_pointer;
+
+ /* build the stack frame on the softirq stack */
+ isp = (u32 *)((char *)irqctx + sizeof(*irqctx));
+
+ __asm__ __volatile__ (
+ "mov r15, r9 \n"
+ "jsr @%0 \n"
+ /* switch to the softirq stack */
+ " mov %1, r15 \n"
+ /* restore the thread stack */
+ "mov r9, r15 \n"
+ : /* no outputs */
+ : "r" (__do_softirq), "r" (isp)
+ : "memory", "r0", "r1", "r2", "r3", "r4",
+ "r5", "r6", "r7", "r8", "r9", "r15", "t", "pr"
+ );
}
#else
static inline void handle_one_irq(unsigned int irq)
diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
index d4840ce..666193f 100644
--- a/arch/sparc/kernel/irq_64.c
+++ b/arch/sparc/kernel/irq_64.c
@@ -698,30 +698,19 @@ void __irq_entry handler_irq(int pil, struct pt_regs *regs)
set_irq_regs(old_regs);
}
-void do_softirq(void)
+void do_softirq_own_stack(void)
{
- unsigned long flags;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
+ void *orig_sp, *sp = softirq_stack[smp_processor_id()];
- if (local_softirq_pending()) {
- void *orig_sp, *sp = softirq_stack[smp_processor_id()];
-
- sp += THREAD_SIZE - 192 - STACK_BIAS;
-
- __asm__ __volatile__("mov %%sp, %0\n\t"
- "mov %1, %%sp"
- : "=&r" (orig_sp)
- : "r" (sp));
- __do_softirq();
- __asm__ __volatile__("mov %0, %%sp"
- : : "r" (orig_sp));
- }
+ sp += THREAD_SIZE - 192 - STACK_BIAS;
- local_irq_restore(flags);
+ __asm__ __volatile__("mov %%sp, %0\n\t"
+ "mov %1, %%sp"
+ : "=&r" (orig_sp)
+ : "r" (sp));
+ __do_softirq();
+ __asm__ __volatile__("mov %0, %%sp"
+ : : "r" (orig_sp));
}
#ifdef CONFIG_HOTPLUG_CPU
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b077f4c..083da7c 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1342,7 +1342,7 @@ bad_gs:
.previous
/* Call softirq on interrupt stack. Interrupts are off. */
-ENTRY(call_softirq)
+ENTRY(do_softirq_own_stack)
CFI_STARTPROC
pushq_cfi %rbp
CFI_REL_OFFSET rbp,0
@@ -1359,7 +1359,7 @@ ENTRY(call_softirq)
decl PER_CPU_VAR(irq_count)
ret
CFI_ENDPROC
-END(call_softirq)
+END(do_softirq_own_stack)
#ifdef CONFIG_XEN
zeroentry xen_hypervisor_callback xen_do_hypervisor_callback
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 4186755..8a5bb01 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -149,35 +149,21 @@ void irq_ctx_init(int cpu)
cpu, per_cpu(hardirq_ctx, cpu), per_cpu(softirq_ctx, cpu));
}
-asmlinkage void do_softirq(void)
+void do_softirq_own_stack(void)
{
- unsigned long flags;
struct thread_info *curctx;
union irq_ctx *irqctx;
u32 *isp;
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
-
- if (local_softirq_pending()) {
- curctx = current_thread_info();
- irqctx = __this_cpu_read(softirq_ctx);
- irqctx->tinfo.task = curctx->task;
- irqctx->tinfo.previous_esp = current_stack_pointer;
-
- /* build the stack frame on the softirq stack */
- isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));
+ curctx = current_thread_info();
+ irqctx = __this_cpu_read(softirq_ctx);
+ irqctx->tinfo.task = curctx->task;
+ irqctx->tinfo.previous_esp = current_stack_pointer;
- call_on_stack(__do_softirq, isp);
- /*
- * Shouldn't happen, we returned above if in_interrupt():
- */
- WARN_ON_ONCE(softirq_count());
- }
+ /* build the stack frame on the softirq stack */
+ isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));
- local_irq_restore(flags);
+ call_on_stack(__do_softirq, isp);
}
bool handle_irq(unsigned irq, struct pt_regs *regs)
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index d04d3ec..4d1c746 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -87,24 +87,3 @@ bool handle_irq(unsigned irq, struct pt_regs *regs)
generic_handle_irq_desc(irq, desc);
return true;
}
-
-
-extern void call_softirq(void);
-
-asmlinkage void do_softirq(void)
-{
- __u32 pending;
- unsigned long flags;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
- pending = local_softirq_pending();
- /* Switch to interrupt stack */
- if (pending) {
- call_softirq();
- WARN_ON_ONCE(softirq_count());
- }
- local_irq_restore(flags);
-}
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 5e865b5..c9e831d 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -19,6 +19,7 @@
#include <linux/atomic.h>
#include <asm/ptrace.h>
+#include <asm/irq.h>
/*
* These correspond to the IORESOURCE_IRQ_* defines in
@@ -374,6 +375,16 @@ struct softirq_action
asmlinkage void do_softirq(void);
asmlinkage void __do_softirq(void);
+
+#ifdef __ARCH_HAS_DO_SOFTIRQ
+void do_softirq_own_stack(void);
+#else
+static inline void do_softirq_own_stack(void)
+{
+ __do_softirq();
+}
+#endif
+
extern void open_softirq(int nr, void (*action)(struct softirq_action *));
extern void softirq_init(void);
extern void __raise_softirq_irqoff(unsigned int nr);
diff --git a/kernel/softirq.c b/kernel/softirq.c
index d7d498d..26ee727 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -29,7 +29,6 @@
#define CREATE_TRACE_POINTS
#include <trace/events/irq.h>
-#include <asm/irq.h>
/*
- No shared variables, all the data are CPU local.
- If a softirq needs serialization, let it serialize itself
@@ -283,7 +282,7 @@ restart:
tsk_restore_flags(current, old_flags, PF_MEMALLOC);
}
-#ifndef __ARCH_HAS_DO_SOFTIRQ
+
asmlinkage void do_softirq(void)
{
@@ -298,13 +297,12 @@ asmlinkage void do_softirq(void)
pending = local_softirq_pending();
if (pending)
- __do_softirq();
+ do_softirq_own_stack();
+ WARN_ON_ONCE(softirq_count());
local_irq_restore(flags);
}
-#endif
-
/*
* Enter an interrupt context.
*/
--
1.8.3.1
On Thu, Sep 26, 2013 at 9:24 AM, Frederic Weisbecker <[email protected]> wrote:
>
> * Turn __ARCH_IRQ_EXIT_ON_IRQ_STACK old ad-hoc style symbol to proper Kconfig
> (CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK)
>
> * Activates it to powerpc as well.
>
> * Fix a bit the changelog of patch 6/8
Ack on the whole series.
I guess x86-64 and powerpc no longer care, but for other architectures
the stack usage issue can be a regression even if I think it's only
been reported on Power. So I'm assuming we should pull this into 3.12.
Yes?
And what about earlier stable kernels? Afaik this was originally
introduced by commit facd8b80c67a, merged into 3.9. Or was there some
other trigger? Do we want to just do the "__do_softirq" ->
"do_softirq()" change for stable?
"Help us, Obi-wan Weisbecker. You are our only hope"
Linus
On Thu, Sep 26, 2013 at 09:43:38AM -0700, Linus Torvalds wrote:
> On Thu, Sep 26, 2013 at 9:24 AM, Frederic Weisbecker <[email protected]> wrote:
> >
> > * Turn __ARCH_IRQ_EXIT_ON_IRQ_STACK old ad-hoc style symbol to proper Kconfig
> > (CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK)
> >
> > * Activates it to powerpc as well.
> >
> > * Fix a bit the changelog of patch 6/8
>
>
> Ack on the whole series.
>
> I guess x86-64 and powerpc no longer care, but for other architectures
> the stack usage issue can be a regression even if I think it's only
> been reported on Power. So I'm assuming we should pull this into 3.12.
> Yes?
>
> And what about earlier stable kernels? Afaik this was originally
> introduced by commit facd8b80c67a, merged into 3.9. Or was there some
> other trigger? Do we want to just do the "__do_softirq" ->
> "do_softirq()" change for stable?
So there is like an underway proposition inside this patchset: the very first commit
has a stable tag on it. This way it can be merged seperately first for 3.12 and
then backported up to the release that has facd8b80c67a.
Then the rest of the series can go for the next merge window in a seperate tree.
Now that's really just one way among possible others to spread the patchset. Because
the regression fix alone unfortunately comes with a performance penalty.
Now if we compare that performance penalty to what we had prior facd8b80c67a, we
were already calling plain do_softirq() on irq_exit() for all archs that had
__ARCH_IRQ_EXIT_IRQS_DISABLED not defined. Namely only arm, arm64, blackfin, s390
were calling __do_softirq() instead. These archs, especially arm, aren't the least
that being said.
We could also backport the part that consolidates to do_softirq_own_stack() and call
it directly if __ARCH_IRQ_EXIT_IRQS_DISABLED. That restores a bit the facd8b80c67a~
state. But it's a bit invasive for post -rc2.
Now may be somebody has some better scenario in mind.
>
> "Help us, Obi-wan Weisbecker. You are our only hope"
"To thy heart thou shalt listen, young Linux maintainer. Then the right merge decision
thou wilt take".
>
> Linus
On Thu, 2013-09-26 at 18:24 +0200, Frederic Weisbecker wrote:
> Now that powerpc runs irq_exit() under the irq stack,
> let the softirq core know about that so that we spare
> the needless stack switch on irq exit's softirq processing.
>
> Signed-off-by: Frederic Weisbecker <[email protected]>
Acked-by: Benjamin Herrenschmidt <[email protected]>
> Cc:
> Paul Mackerras <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: H. Peter Anvin <[email protected]>
> Cc: Linus Torvalds <[email protected]>
> Cc: Paul Mackerras <[email protected]>
> Cc: James Hogan <[email protected]>
> Cc: James E.J. Bottomley <[email protected]>
> Cc: Helge Deller <[email protected]>
> Cc: Martin Schwidefsky <[email protected]>
> Cc: Heiko Carstens <[email protected]>
> Cc: David S. Miller <[email protected]>
> Cc: Andrew Morton <[email protected]>
> ---
> arch/powerpc/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 38f3b7e..b365d5c 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -138,6 +138,7 @@ config PPC
> select OLD_SIGSUSPEND
> select OLD_SIGACTION if PPC32
> select HAVE_DEBUG_STACKOVERFLOW
> + select HAVE_IRQ_EXIT_ON_IRQ_STACK
>
> config EARLY_PRINTK
> bool
On Thu, Sep 26, 2013 at 09:43:38AM -0700, Linus Torvalds wrote:
> On Thu, Sep 26, 2013 at 9:24 AM, Frederic Weisbecker <[email protected]> wrote:
> >
> > * Turn __ARCH_IRQ_EXIT_ON_IRQ_STACK old ad-hoc style symbol to proper Kconfig
> > (CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK)
> >
> > * Activates it to powerpc as well.
> >
> > * Fix a bit the changelog of patch 6/8
>
>
> Ack on the whole series.
>
> I guess x86-64 and powerpc no longer care, but for other architectures
> the stack usage issue can be a regression even if I think it's only
> been reported on Power. So I'm assuming we should pull this into 3.12.
> Yes?
>
> And what about earlier stable kernels? Afaik this was originally
> introduced by commit facd8b80c67a, merged into 3.9. Or was there some
> other trigger? Do we want to just do the "__do_softirq" ->
> "do_softirq()" change for stable?
>
> "Help us, Obi-wan Weisbecker. You are our only hope"
Ok, I'm going to split that in two pull requests for Ingo and Thomas.
One for the 1st patch as a regression fix to be applied for 3.12 and backported.
Another one for the rest of the series to be applied on the next merge window.
If anybody oppose, please tell.
Thanks.