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 <redacted>

Reviewed-by: Michael Lyle <redacted>