Re: [PATCH v3 03/13] bcache: set task properly in allocator_wait()

[Coly Li <colyli@suse.de>]

On 16/01/2018 5:05 PM, Hannes Reinecke wrote:
> On 01/14/2018 03:42 PM, 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. Here is the code block,
>>
>> 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);                            \
>>
>> 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]".
>>
>> This patch fixes this problem by setting task state to TASK_RUNNING if
>> kthread_should_stop() is true and before kernel thread returns back to
>> kernel/kthread.s:kthread().
>>
>> Changelog:
>> v2: fix the race issue in v1 patch.
>> v1: initial buggy fix.
>>
>> Signed-off-by: Coly Li <colyli@suse.de>
>> Cc: Michael Lyle <mlyle@lyle.org>
>> Cc: Hannes Reinecke <hare@suse.de>
>> Cc: Junhui Tang <tang.junhui@zte.com.cn>
>> ---
>>  drivers/md/bcache/alloc.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
>> index 6cc6c0f9c3a9..458e1d38577d 100644
>> --- a/drivers/md/bcache/alloc.c
>> +++ b/drivers/md/bcache/alloc.c
>> @@ -287,8 +287,10 @@ do {									\
>>  			break;						\
>>  									\
>>  		mutex_unlock(&(ca)->set->bucket_lock);			\
>> -		if (kthread_should_stop())				\
>> +		if (kthread_should_stop()) {				\
>> +			set_current_state(TASK_RUNNING);		\
>>  			return 0;					\
>> +		}							\
>>  									\
>>  		schedule();						\
>>  		mutex_lock(&(ca)->set->bucket_lock);			\
>>
> Might be an idea to merge it with the previous patch.
> 
> Other than that:
> 
> Reviewed-by: Hannes Reinecke <hare@suse.com>

Hi Hannes,

Sure, I will do that in v4 patche set. Thanks for the review.

Coly Li