writeback: do not lose wake-ups in bdi threads

Currently, bdi threads ('bdi_writeback_thread()') can lose wake-ups. For
example, if 'bdi_queue_work()' is executed after the bdi thread have had
finished 'wb_do_writeback()' but before it called
'schedule_timeout_interruptible()'.

To fix this issue, we have to check whether we have works to process after we
have changed the task state to 'TASK_INTERRUPTIBLE'.

This patch also clean-ups handling of the cases when 'dirty_writeback_interval'
is zero or non-zero.

Additionally, this patch also removes unneeded 'list_empty_careful()' call.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 9 insertions, 8 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 002be0ff2ab3..05444eaa3f36 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -848,17 +848,18 @@ int bdi_writeback_thread(void *data)
                                 break;
                 }
 
-                if (dirty_writeback_interval) {
-                        wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
-                        schedule_timeout_interruptible(wait_jiffies);
-                } else {
-                        set_current_state(TASK_INTERRUPTIBLE);
-                        if (list_empty_careful(&wb->bdi->work_list) &&
-                            !kthread_should_stop())
-                                schedule();
+                set_current_state(TASK_INTERRUPTIBLE);
+                if (!list_empty(&bdi->work_list)) {
                         __set_current_state(TASK_RUNNING);
+                        continue;
                 }
 
+                if (dirty_writeback_interval) {
+                        wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
+                        schedule_timeout(wait_jiffies);
+                } else
+                        schedule();
+
                 try_to_freeze();
         }