diff options
authorJan Kara <>2018-05-03 18:26:26 +0200
committerJens Axboe <>2018-05-03 16:11:37 -0600
commitb8b784958eccbf8f51ebeee65282ca3fd59ea391 (patch)
parent8bfc3b4c6f9de815de4ab73784b9419348266a65 (diff)
bdi: Fix oops in wb_workfn()for-linus-20180504
Syzbot has reported that it can hit a NULL pointer dereference in wb_workfn() due to wb->bdi->dev being NULL. This indicates that wb_workfn() was called for an already unregistered bdi which should not happen as wb_shutdown() called from bdi_unregister() should make sure all pending writeback works are completed before bdi is unregistered. Except that wb_workfn() itself can requeue the work with: mod_delayed_work(bdi_wq, &wb->dwork, 0); and if this happens while wb_shutdown() is waiting in: flush_delayed_work(&wb->dwork); the dwork can get executed after wb_shutdown() has finished and bdi_unregister() has cleared wb->bdi->dev. Make wb_workfn() use wakeup_wb() for requeueing the work which takes all the necessary precautions against racing with bdi unregistration. CC: Tetsuo Handa <> CC: Tejun Heo <> Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 Reported-by: syzbot <> Reviewed-by: Dave Chinner <> Signed-off-by: Jan Kara <> Signed-off-by: Jens Axboe <>
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 47d7c151fcba..471d863958bc 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work)
if (!list_empty(&wb->work_list))
- mod_delayed_work(bdi_wq, &wb->dwork, 0);
+ wb_wakeup(wb);
else if (wb_has_dirty_io(wb) && dirty_writeback_interval)