Re: [PATCH 1/1] sched/core: Fix stuck on completion for affine_move_task() when stopper disable

[Peter Zijlstra]

On Wed, Sep 27, 2023 at 11:34:28AM +0800, Kuyo Chang wrote:
> From: kuyo chang <kuyo.chang@xxxxxxxxxxxx>
> 
> [Syndrome] hung detect shows below warning msg
> [ 4320.666557] [   T56] khungtaskd: [name:hung_task&]INFO: task stressapptest:17803 blocked for more than 3600 seconds.
> [ 4320.666589] [   T56] khungtaskd: [name:core&]task:stressapptest   state:D stack:0     pid:17803 ppid:17579  flags:0x04000008
> [ 4320.666601] [   T56] khungtaskd: Call trace:
> [ 4320.666607] [   T56] khungtaskd:  __switch_to+0x17c/0x338
> [ 4320.666642] [   T56] khungtaskd:  __schedule+0x54c/0x8ec
> [ 4320.666651] [   T56] khungtaskd:  schedule+0x74/0xd4
> [ 4320.666656] [   T56] khungtaskd:  schedule_timeout+0x34/0x108
> [ 4320.666672] [   T56] khungtaskd:  do_wait_for_common+0xe0/0x154
> [ 4320.666678] [   T56] khungtaskd:  wait_for_completion+0x44/0x58
> [ 4320.666681] [   T56] khungtaskd:  __set_cpus_allowed_ptr_locked+0x344/0x730
> [ 4320.666702] [   T56] khungtaskd:  __sched_setaffinity+0x118/0x160
> [ 4320.666709] [   T56] khungtaskd:  sched_setaffinity+0x10c/0x248
> [ 4320.666715] [   T56] khungtaskd:  __arm64_sys_sched_setaffinity+0x15c/0x1c0
> [ 4320.666719] [   T56] khungtaskd:  invoke_syscall+0x3c/0xf8
> [ 4320.666743] [   T56] khungtaskd:  el0_svc_common+0xb0/0xe8
> [ 4320.666749] [   T56] khungtaskd:  do_el0_svc+0x28/0xa8
> [ 4320.666755] [   T56] khungtaskd:  el0_svc+0x28/0x9c
> [ 4320.666761] [   T56] khungtaskd:  el0t_64_sync_handler+0x7c/0xe4
> [ 4320.666766] [   T56] khungtaskd:  el0t_64_sync+0x18c/0x190
> 
> [Analysis]
> 
> After add some debug footprint massage, this issue happened at stopper
> disable case.
> It cannot exec migration_cpu_stop fun to complete migration.
> This will cause stuck on wait_for_completion.

How did you get in this situation?

> Signed-off-by: kuyo chang <kuyo.chang@xxxxxxxxxxxx>
> ---
>  kernel/sched/core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1dc0b0287e30..98c217a1caa0 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3041,8 +3041,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
>  		task_rq_unlock(rq, p, rf);
>  
>  		if (!stop_pending) {
> -			stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
> -					    &pending->arg, &pending->stop_work);
> +			if (!stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
> +					    &pending->arg, &pending->stop_work))
> +				return -ENOENT;

And -ENOENT is the right return code for when the target CPU is not
available?

I suspect you're missing more than halp the picture and this is a
band-aid solution at best. Please try harder.

>  		}
>  
>  		if (flags & SCA_MIGRATE_ENABLE)
> -- 
> 2.18.0
>