2014-07-29 09:24:57

by Wanpeng Li

Subject: [PATCH v4] x86, hotplug: fix llc shared map unreleased during cpu hotplug

BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
IP: [..] find_busiest_group
PGD 5a9d5067 PUD 13067 PMD 0
Oops: 0000 [#3] SMP
[...]
Call Trace:
load_balance
? _raw_spin_unlock_irqrestore
idle_balance
__schedule
schedule
schedule_timeout
? lock_timer_base
schedule_timeout_uninterruptible
msleep
lock_device_hotplug_sysfs
online_store
dev_attr_store
sysfs_write_file
vfs_write
SyS_write
system_call_fastpath

Last level cache shared map is built during cpu up and build sched domain
routine takes advantage of it to setup sched domain cpu topology, however,
llc shared map is unreleased during cpu disable which lead to invalid sched
domain cpu topology. This patch fix it by release llc shared map correctly
during cpu disable.

Reviewed-by: Yasuaki Ishimatsu <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
v1 -> v2:
* fix subject line
v2 -> v3:
* simplify backtrace

arch/x86/kernel/smpboot.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 5492798..0134ec7 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1292,6 +1292,9 @@ static void remove_siblinginfo(int cpu)

for_each_cpu(sibling, cpu_sibling_mask(cpu))
cpumask_clear_cpu(cpu, cpu_sibling_mask(sibling));
+ for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
+ cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
+ cpumask_clear(cpu_llc_shared_mask(cpu));
cpumask_clear(cpu_sibling_mask(cpu));
cpumask_clear(cpu_core_mask(cpu));
c->phys_proc_id = 0;
--
1.9.1

2014-07-29 17:28:46

by Toshi Kani

Subject: Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during cpu hotplug

On Tue, 2014-07-29 at 17:24 +0800, Wanpeng Li wrote:
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
> IP: [..] find_busiest_group
> PGD 5a9d5067 PUD 13067 PMD 0
> Oops: 0000 [#3] SMP
> [...]
> Call Trace:
> load_balance
> ? _raw_spin_unlock_irqrestore
> idle_balance
> __schedule
> schedule
> schedule_timeout
> ? lock_timer_base
> schedule_timeout_uninterruptible
> msleep
> lock_device_hotplug_sysfs
> online_store
> dev_attr_store
> sysfs_write_file
> vfs_write
> SyS_write
> system_call_fastpath
>
> Last level cache shared map is built during cpu up and build sched domain
> routine takes advantage of it to setup sched domain cpu topology, however,
> llc shared map is unreleased during cpu disable which lead to invalid sched
> domain cpu topology. This patch fix it by release llc shared map correctly
> during cpu disable.
>
> Reviewed-by: Yasuaki Ishimatsu <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>

The change looks good to me.

Reviewed-by: Toshi Kani <[email protected]>

Thanks,
-Toshi