Re: [peterz-queue:sched/core] [sched/fair] 420356c350: WARNING:at_kernel/sched/core.c:#__might_sleep

[Chen Yu <yu.c.chen@intel.com>]

On 2024-08-17 at 11:33:29 +0200, Peter Zijlstra wrote:
> On Fri, Aug 16, 2024 at 05:15:12PM +0800, kernel test robot wrote:
> > kernel test robot noticed "WARNING:at_kernel/sched/core.c:#__might_sleep" on:
> > 
> > commit: 420356c3504091f0f6021974389df7c58f365dad ("sched/fair: Implement delayed dequeue")
> > https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git sched/core
> 
> > [   86.252370][  T674] ------------[ cut here ]------------
> > [ 86.252945][ T674] do not call blocking ops when !TASK_RUNNING; state=1 set at kthread_worker_fn (kernel/kthread.c:?) 
> > [ 86.254001][ T674] WARNING: CPU: 1 PID: 674 at kernel/sched/core.c:8469 __might_sleep (kernel/sched/core.c:8465) 
> 
> > [ 86.283398][ T674] ? handle_bug (arch/x86/kernel/traps.c:239) 
> > [ 86.283995][ T674] ? exc_invalid_op (arch/x86/kernel/traps.c:260) 
> > [ 86.284787][ T674] ? asm_exc_invalid_op (arch/x86/include/asm/idtentry.h:621) 
> > [ 86.285682][ T674] ? __might_sleep (kernel/sched/core.c:8465) 
> > [ 86.286380][ T674] ? __might_sleep (kernel/sched/core.c:8465) 
> > [ 86.287116][ T674] kthread_worker_fn (include/linux/kernel.h:73 include/linux/freezer.h:53 kernel/kthread.c:851) 
> > [ 86.287701][ T674] ? kthread_worker_fn (kernel/kthread.c:?) 
> > [ 86.288138][ T674] kthread (kernel/kthread.c:391) 
> > [ 86.288482][ T674] ? __cfi_kthread_worker_fn (kernel/kthread.c:803) 
> > [ 86.288951][ T674] ? __cfi_kthread (kernel/kthread.c:342) 
> > [ 86.289560][ T674] ret_from_fork (arch/x86/kernel/process.c:153) 
> > [ 86.290162][ T674] ? __cfi_kthread (kernel/kthread.c:342) 
> > [ 86.291465][ T674] ret_from_fork_asm (arch/x86/entry/entry_64.S:254) 
> 
> AFAICT this is a pre-existing issue. Notably that all transcribes to:
> 
> kthread_worker_fn()
>   ...
> repeat:
>   set_current_state(TASK_INTERRUPTIBLE);
>   ...
>   if (work) { // false
>     __set_current_state(TASK_RUNNING);
>     ...
>   } else if (!freezing(current)) // false -- we are freezing
>     schedule();
> 
>   // so state really is still TASK_INTERRUPTIBLE here
>   try_to_freeze()
>     might_sleep() <--- boom, per the above.
>

Would the following fix make sense?

diff --git a/kernel/kthread.c b/kernel/kthread.c
index f7be976ff88a..09850b2109c9 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -848,6 +848,12 @@ int kthread_worker_fn(void *worker_ptr)
 	} else if (!freezing(current))
 		schedule();
 
+	/*
+	 * Explictly set the running state in case we are being frozen
+	 * and skip the schedule() above. try_to_freeze() expects the
+	 * current task to be in running state.
+	 */
+	__set_current_state(TASK_RUNNING);
 	try_to_freeze();
 	cond_resched();
 	goto repeat;
-- 
2.25.1

Hi Oliver,
Could you please help check if above change would make the warning go away?

thanks,
Chenyu