Re: [WARNING] kernel/workqueue.c:2041 process_one_work (when cpu goes offline)

[Tejun Heo]

Hello, Steven.

On Wed, Apr 05, 2017 at 03:16:28PM -0400, Steven Rostedt wrote:
> My tests have started to recently trigger this warning quite often,
> which causes my tests to fail. The test that triggers this is running
> the mmiotracer which forces all but one CPU offline.
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 6 at /work/autotest/nobackup/linux-test.git/kernel/workqueue.c:2041 process_one_work+0x90/0x485
> Modules linked in: ppdev parport_pc parport [last unloaded: trace_events_sample]
> CPU: 0 PID: 6 Comm: vmstat Not tainted 4.11.0-rc5-test+ #3
> Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014
> Call Trace:
>  dump_stack+0x68/0x92
>  __warn+0xc2/0xdd
>  warn_slowpath_null+0x1d/0x1f
>  process_one_work+0x90/0x485
>  process_scheduled_works+0x2c/0x33
>  rescuer_thread+0x19c/0x295
>  ? process_scheduled_works+0x33/0x33
>  kthread+0xf4/0xf9
>  ? __list_del_entry+0x22/0x22
>  ret_from_fork+0x2e/0x40
> ---[ end trace ed53fc9d3ce10aa8 ]---
> 
> #ifdef CONFIG_LOCKDEP
> 	/*
> 	 * It is permissible to free the struct work_struct from
> 	 * inside the function that is called from it, this we need to
> 	 * take into account for lockdep too.  To avoid bogus "held
> 	 * lock freed" warnings as well as problems when looking into
> 	 * work->lockdep_map, make a copy and use that here.
> 	 */
> 	struct lockdep_map lockdep_map;
> 
> 	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
> #endif
> 	/* ensure we're on the correct CPU */
> 	WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&   <<--- line 2041
> 		     raw_smp_processor_id() != pool->cpu);
> 
> 	/*
> 	 * A single work shouldn't be executed concurrently by
> 	 * multiple workers on a single cpu.  Check whether anyone is
> 	 * already processing the work.  If so, defer the work to the
> 	 * currently executing one.
> 	 */
> 
> 
> I'm assuming that this thread was migrated due to the CPU offlining and
> causes pool->cpu not to equal raw_smp_processor_id(). Or should that
> not be happening?

If this happens while CPU is going donw, the pool should have
POOL_DISASSOCIATED set by that point and the actual affinity shouldn't
matter.  Maybe I messed up the rescuer part of it.  I'll look into it.

Thanks.

-- 
tejun