writeback: do not lose wake-ups in the forker thread - 2

Currently, if someone submits jobs for the default bdi, we can lose wake-up
events. E.g., this can happen if 'bdi_queue_work()' is called when
'bdi_forker_thread()' is executing code after 'wb_do_writeback(me, 0)', but
before 'set_current_state(TASK_INTERRUPTIBLE)'.

This situation is unlikely, and the result is not very severe - we'll just
delay the execution of the work, but this is still not very nice.

This patch fixes the issue by checking whether the default bdi has works before
the forker thread goes sleep.

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

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b1dc2d4b9cddc5ef2057ba49a26a9b084cbd0e94..72e6eb96efe21f572a9caac092722512bde2b9df 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -358,6 +358,10 @@ static int bdi_forker_thread(void *ptr)
                        bdi_add_default_flusher_thread(bdi);
                }
 
+               /* Keep working if default bdi still has things to do */
+               if (!list_empty(&me->bdi->work_list))
+                       __set_current_state(TASK_RUNNING);
+
                if (list_empty(&bdi_pending_list)) {
                        unsigned long wait;