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

tang.junhui
2018-01-03T18:29:37Z

From: Tang Junhui <tang.junhui@zte.com.cn>

LGTM.

Reviewed-by: Tang Junhui <tang.junhui@zte.com.cn>

>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>
>---
> 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)
>--
>2.15.1

Thanks,
Tang Junhui