Re: [PATCH] Do not change worker's running cpu in cmci_rediscover().

From: Tang Chen
Date: Mon Oct 08 2012 - 01:46:24 EST

Hi all,

Would you please help to review this patch ?

Thanks. :)


On 09/28/2012 03:54 PM, Lai Jiangshan wrote:
Add CC: Tejun Heo, Peter Zijlstra.

Hi, Tejun

This is a bug whose root cause is the same as
https://bugzilla.kernel.org/show_bug.cgi?id=47301.

Acked-by: Lai Jiangshan<laijs@xxxxxxxxxxxxxx>

thanks,
Lai


On 09/27/2012 05:19 PM, Tang Chen wrote:
1. cmci_rediscover() is only called by the CPU_POST_DEAD event handler, which
means the corresponding cpu has already dead. As a result, it won't be accessed
in the for_each_online_cpu loop.
So, we could change the if(cpu == dying) statement into a BUG_ON().

2. cmci_rediscover() used set_cpus_allowed_ptr() to change the current process's
running cpu, and migrate itself to the dest cpu. But worker processes are not
allowed to be migrated. If current is a worker, the worker will be migrated to
another cpu, but the corresponding worker_pool is still on the original cpu.

In this case, the following BUG_ON in try_to_wake_up_local() will be triggered:
BUG_ON(rq != this_rq());

This will cause the kernel panic.

This patch removes the set_cpus_allowed_ptr() call, and put the cmci rediscover
jobs onto all the other cpus using system_wq. This could bring some delay for
the jobs.

The following is call trace.

[ 6155.451107] ------------[ cut here ]------------
[ 6155.452019] kernel BUG at kernel/sched/core.c:1654!
......
[ 6155.452019] RIP: 0010:[<ffffffff810add15>] [<ffffffff810add15>] try_to_wake_up_local+0x115/0x130
......
[ 6155.452019] Call Trace:
[ 6155.452019] [<ffffffff8166fc14>] __schedule+0x764/0x880
[ 6155.452019] [<ffffffff81670059>] schedule+0x29/0x70
[ 6155.452019] [<ffffffff8166de65>] schedule_timeout+0x235/0x2d0
[ 6155.452019] [<ffffffff810db57d>] ? mark_held_locks+0x8d/0x140
[ 6155.452019] [<ffffffff810dd463>] ? __lock_release+0x133/0x1a0
[ 6155.452019] [<ffffffff81671c50>] ? _raw_spin_unlock_irq+0x30/0x50
[ 6155.452019] [<ffffffff810db8f5>] ? trace_hardirqs_on_caller+0x105/0x190
[ 6155.452019] [<ffffffff8166fefb>] wait_for_common+0x12b/0x180
[ 6155.452019] [<ffffffff810b0b30>] ? try_to_wake_up+0x2f0/0x2f0
[ 6155.452019] [<ffffffff8167002d>] wait_for_completion+0x1d/0x20
[ 6155.452019] [<ffffffff8110008a>] stop_one_cpu+0x8a/0xc0
[ 6155.452019] [<ffffffff810abd40>] ? __migrate_task+0x1a0/0x1a0
[ 6155.452019] [<ffffffff810a6ab8>] ? complete+0x28/0x60
[ 6155.452019] [<ffffffff810b0fd8>] set_cpus_allowed_ptr+0x128/0x130
[ 6155.452019] [<ffffffff81036785>] cmci_rediscover+0xf5/0x140
[ 6155.452019] [<ffffffff816643c0>] mce_cpu_callback+0x18d/0x19d
[ 6155.452019] [<ffffffff81676187>] notifier_call_chain+0x67/0x150
[ 6155.452019] [<ffffffff810a03de>] __raw_notifier_call_chain+0xe/0x10
[ 6155.452019] [<ffffffff81070470>] __cpu_notify+0x20/0x40
[ 6155.452019] [<ffffffff810704a5>] cpu_notify_nofail+0x15/0x30
[ 6155.452019] [<ffffffff81655182>] _cpu_down+0x262/0x2e0
[ 6155.452019] [<ffffffff81655236>] cpu_down+0x36/0x50
[ 6155.452019] [<ffffffff813d3eaa>] acpi_processor_remove+0x50/0x11e
[ 6155.452019] [<ffffffff813a6978>] acpi_device_remove+0x90/0xb2
[ 6155.452019] [<ffffffff8143cbec>] __device_release_driver+0x7c/0xf0
[ 6155.452019] [<ffffffff8143cd6f>] device_release_driver+0x2f/0x50
[ 6155.452019] [<ffffffff813a7870>] acpi_bus_remove+0x32/0x6d
[ 6155.452019] [<ffffffff813a7932>] acpi_bus_trim+0x87/0xee
[ 6155.452019] [<ffffffff813a7a21>] acpi_bus_hot_remove_device+0x88/0x16b
[ 6155.452019] [<ffffffff813a33ee>] acpi_os_execute_deferred+0x27/0x34
[ 6155.452019] [<ffffffff81090589>] process_one_work+0x219/0x680
[ 6155.452019] [<ffffffff81090528>] ? process_one_work+0x1b8/0x680
[ 6155.452019] [<ffffffff813a33c7>] ? acpi_os_wait_events_complete+0x23/0x23
[ 6155.452019] [<ffffffff810923be>] worker_thread+0x12e/0x320
[ 6155.452019] [<ffffffff81092290>] ? manage_workers+0x110/0x110
[ 6155.452019] [<ffffffff81098396>] kthread+0xc6/0xd0
[ 6155.452019] [<ffffffff8167c4c4>] kernel_thread_helper+0x4/0x10
[ 6155.452019] [<ffffffff81671f30>] ? retint_restore_args+0x13/0x13
[ 6155.452019] [<ffffffff810982d0>] ? __init_kthread_worker+0x70/0x70
[ 6155.452019] [<ffffffff8167c4c0>] ? gs_change+0x13/0x13

Signed-off-by: Tang Chen<tangchen@xxxxxxxxxxxxxx>
Signed-off-by: Miao Xie<miaox@xxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/mcheck/mce_intel.c | 34 +++++++++++++++++--------------
1 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_intel.c b/arch/x86/kernel/cpu/mcheck/mce_intel.c
index 38e49bc..f7d9795 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_intel.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_intel.c
@@ -163,34 +163,38 @@ void cmci_clear(void)
raw_spin_unlock_irqrestore(&cmci_discover_lock, flags);
}

+static long cmci_rediscover_work_func(void *arg)
+{
+ int banks;
+
+ /* Recheck banks in case CPUs don't all have the same */
+ if (cmci_supported(&banks))
+ cmci_discover(banks, 0);
+
+ return 0;
+}
+
/*
* After a CPU went down cycle through all the others and rediscover
* Must run in process context.
*/
void cmci_rediscover(int dying)
{
- int banks;
- int cpu;
- cpumask_var_t old;
+ int cpu, banks;

if (!cmci_supported(&banks))
return;
- if (!alloc_cpumask_var(&old, GFP_KERNEL))
- return;
- cpumask_copy(old,&current->cpus_allowed);

for_each_online_cpu(cpu) {
- if (cpu == dying)
- continue;
- if (set_cpus_allowed_ptr(current, cpumask_of(cpu)))
+ BUG_ON(cpu == dying);
+
+ if (cpu == smp_processor_id()) {
+ cmci_rediscover_work_func(NULL);
continue;
- /* Recheck banks in case CPUs don't all have the same */
- if (cmci_supported(&banks))
- cmci_discover(banks, 0);
- }
+ }

- set_cpus_allowed_ptr(current, old);
- free_cpumask_var(old);
+ work_on_cpu(cpu, cmci_rediscover_work_func, NULL);
+ }
}

/*



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