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

Coly Li
2018-01-03T14:03:54Z

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