Re: [PATCH v1 01/10] bcache: exit bch_writeback_thread() with proper task state

[Michael Lyle <mlyle@lyle.org>]

On 01/03/2018 06:03 AM, Coly Li wrote:
> Kernel thread routine bch_writeback_thread() has the following code block,
> 
> 452                         set_current_state(TASK_INTERRUPTIBLE);
> 453
> 454                         if (kthread_should_stop())
> 455                                 return 0;
> 456
> 457                         schedule();
> 458                         continue;
> 
> At line 452, its status is set to TASK_INTERRUPTIBLE, and at line 454 if
> kthread_should_stop() is true, a "return 0" at line 455 will to function
> kernel/kthread.c:kthread() and call do_exit().
> 
> It is not good to enter do_exit() with task state TASK_INTERRUPTIBLE, in
> following code path might_sleep() is called and a warning message is
> reported by __might_sleep(): "WARNING: do not call blocking ops when
> !TASK_RUNNING; state=1 set at [xxxx]".
> 
> Indeed it does not hurt when kernel thread exits with TASK_INTERRUPTIBLE
> state, but this warning message scares users, makes them feel there might
> be something risky with bcache and hurt their data.
> 
> In this patch, TASK_INTERRUPTIBLE is set after kthread_should_stop(),
> so writeback kernel thread can exist and enter do_exit() with
> TASK_RUNNING state. Warning message from might_sleep() is removed.
> 
> Signed-off-by: Coly Li <colyli@suse.de>

Reviewed-by: Michael Lyle <mlyle@lyle.org>