[PATCH v1 01/10] bcache: exit bch_writeback_thread() with proper task state

Coly Li
2018-01-03T14:03:16Z

Kernel thread routine bch_writeback_thread() has the following code block,

452 set_current_state(TASK_INTERRUPTIBLE);
453
454 if (kthread_should_stop())
455 return 0;
456
457 schedule();
458 continue;

At line 452, its status is set to TASK_INTERRUPTIBLE, and at line 454 if
kthread_should_stop() is true, a "return 0" at line 455 will to function
kernel/kthread.c:kthread() and call do_exit().

It is not good to enter do_exit() with task state TASK_INTERRUPTIBLE, in
following code path might_sleep() is called and a warning message is
reported by __might_sleep(): "WARNING: do not call blocking ops when
!TASK_RUNNING; state=1 set at [xxxx]".

Indeed it does not hurt when kernel thread exits with TASK_INTERRUPTIBLE
state, but this warning message scares users, makes them feel there might
be something risky with bcache and hurt their data.

In this patch, TASK_INTERRUPTIBLE is set after kthread_should_stop(),
so writeback kernel thread can exist and enter do_exit() with
TASK_RUNNING state. Warning message from might_sleep() is removed.

Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/bcache/writeback.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 56a37884ca8b..a57149803df6 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -449,11 +449,11 @@ static int bch_writeback_thread(void *arg)
(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
!dc->writeback_running)) {
up_write(&dc->writeback_lock);
- set_current_state(TASK_INTERRUPTIBLE);

if (kthread_should_stop())
return 0;

+ set_current_state(TASK_INTERRUPTIBLE);
schedule();
continue;
}
--
2.15.1