mm: Add comment explaining task state setting in bdi_forker_thread()

CC: Wu Fengguang <fengguang.wu@intel.com>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 94a047bb6c3..a87da524a4a 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -401,6 +401,13 @@ static int bdi_forker_thread(void *ptr)
                 }
 
                 spin_lock_bh(&bdi_lock);
+                /*
+                 * In the following loop we are going to check whether we have
+                 * some work to do without any synchronization with tasks
+                 * waking us up to do work for them. So we have to set task
+                 * state already here so that we don't miss wakeups coming
+                 * after we verify some condition.
+                 */
                 set_current_state(TASK_INTERRUPTIBLE);
 
                 list_for_each_entry(bdi, &bdi_list, bdi_list) {