On 01/03/2018 03:03 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.
>
> 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@xxxxxxx>
> ---
> drivers/md/bcache/alloc.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
> index a0cc1bc6d884..48c002faf08d 100644
> --- a/drivers/md/bcache/alloc.c
> +++ b/drivers/md/bcache/alloc.c
> @@ -282,7 +282,6 @@ static void invalidate_buckets(struct cache *ca)
> #define allocator_wait(ca, cond) \
> do { \
> while (1) { \
> - set_current_state(TASK_INTERRUPTIBLE); \
> if (cond) \
> break; \
> \
> @@ -290,10 +289,10 @@ do { \
> if (kthread_should_stop()) \
> return 0; \
> \
> + set_current_state(TASK_INTERRUPTIBLE); \
> schedule(); \
> mutex_lock(&(ca)->set->bucket_lock); \
> } \
> - __set_current_state(TASK_RUNNING); \
> } while (0)
>
> static int bch_allocator_push(struct cache *ca, long bucket)
>
Same as with the previous patch; why not simply set it to TASK_RUNNING
before 'return 0' ?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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