diff options
authorColy Li <>2018-02-07 11:41:41 -0800
committerJens Axboe <>2018-02-07 12:50:01 -0700
commit99361bbf26337186f02561109c17a4c4b1a7536a (patch)
parentc4dc2497d50d9c6fb16aa0d07b6a14f3b2adb1e0 (diff)
bcache: properly set task state in bch_writeback_thread()
Kernel thread routine bch_writeback_thread() has the following code block, 447 down_write(&dc->writeback_lock); 448~450 if (check conditions) { 451 up_write(&dc->writeback_lock); 452 set_current_state(TASK_INTERRUPTIBLE); 453 454 if (kthread_should_stop()) 455 return 0; 456 457 schedule(); 458 continue; 459 } If condition check is true, its task state is set to TASK_INTERRUPTIBLE and call schedule() to wait for others to wake up it. There are 2 issues in current code, 1, Task state is set to TASK_INTERRUPTIBLE after the condition checks, if another process changes the condition and call wake_up_process(dc-> writeback_thread), then at line 452 task state is set back to TASK_INTERRUPTIBLE, the writeback kernel thread will lose a chance to be waken up. 2, At line 454 if kthread_should_stop() is true, writeback kernel thread will return to kernel/kthread.c:kthread() with TASK_INTERRUPTIBLE 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]". For the first issue, task state should be set before condition checks. Ineed because dc->writeback_lock is required when modifying all the conditions, calling set_current_state() inside code block where dc-> writeback_lock is hold is safe. But this is quite implicit, so I still move set_current_state() before all the condition checks. For the second issue, frankley speaking 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. Setting task state to TASK_RUNNING before returning fixes this problem. In alloc.c:allocator_wait(), there is also a similar issue, and is also fixed in this patch. Changelog: v3: merge two similar fixes into one patch v2: fix the race issue in v1 patch. v1: initial buggy fix. Signed-off-by: Coly Li <> Reviewed-by: Hannes Reinecke <> Reviewed-by: Michael Lyle <> Cc: Michael Lyle <> Cc: Junhui Tang <> Signed-off-by: Jens Axboe <>
2 files changed, 8 insertions, 3 deletions
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); \
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 51306a19ab03..58218f7e77c3 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -564,18 +564,21 @@ static int bch_writeback_thread(void *arg)
while (!kthread_should_stop()) {
+ set_current_state(TASK_INTERRUPTIBLE);
if (!atomic_read(&dc->has_dirty) ||
(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
!dc->writeback_running)) {
- set_current_state(TASK_INTERRUPTIBLE);
- if (kthread_should_stop())
+ if (kthread_should_stop()) {
+ set_current_state(TASK_RUNNING);
return 0;
+ }
+ set_current_state(TASK_RUNNING);
searched_full_index = refill_dirty(dc);