Re: [PATCH v1 02/10] bcache: set task properly in allocator_wait()

Michael Lyle
2018-01-03T17:09:21Z

On 01/03/2018 06:03 AM, Coly Li wrote:
> Kernel thread routine bch_allocator_thread() references macro
> allocator_wait() to wait for a condition or quit to do_exit()
> when kthread_should_stop() is true.
>
> Macro allocator_wait() has 2 issues in setting task state, let's
> see its code piece,
>
> 284 while (1) { \
> 285 set_current_state(TASK_INTERRUPTIBLE); \
> 286 if (cond) \
> 287 break; \
> 288 \
> 289 mutex_unlock(&(ca)->set->bucket_lock); \
> 290 if (kthread_should_stop()) \
> 291 return 0; \
> 292 \
> 293 schedule(); \
> 294 mutex_lock(&(ca)->set->bucket_lock); \
> 295 } \
> 296 __set_current_state(TASK_RUNNING); \
>
> 1) At line 285, task state is set to TASK_INTERRUPTIBLE, if at line 290
> kthread_should_stop() is true, the kernel thread will terminate and return
> to kernel/kthread.s:kthread(), then calls do_exit() with TASK_INTERRUPTIBLE
> state. This is not a suggested behavior and a warning message will be
> reported by might_sleep() in do_exit() code path: "WARNING: do not call
> blocking ops when !TASK_RUNNING; state=1 set at [xxxx]".
>
> 2) Because task state is set to TASK_INTERRUPTIBLE at line 285, when break
> while-loop the task state has to be set back to TASK_RUNNING at line 296.
> Indeed it is unncessary, if task state is set to TASK_INTERRUPTIBLE before
> calling schedule() at line 293, we don't need to set the state back to
> TASK_RUNNING at line 296 anymore. The reason is, allocator kthread is only
> woken up by wake_up_process(), this routine makes sure the task state of
> allocator kthread will be TASK_RUNNING after it returns from schedule() at
> line 294 (see kernel/sched/core.c:try_to_wake_up() for more detailed
> information).
>
> This patch fixes the above 2 issues by,
> 1) Setting TASK_INTERRUPTIBLE state just before calling schedule().
> 2) Then setting TASK_RUNNING at line 296 is unnecessary, remove it.
>
> Signed-off-by: Coly Li <colyli@suse.de>

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