From 1ef7d9aa32a8ee054c4d4fdcd2ea537c04d61b2f Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Tue, 15 Sep 2009 21:37:55 +0200 Subject: [PATCH] writeback: fix possible bdi writeback refcounting problem wb_clear_pending AFAIKS should not be called after the item has been put on the list, except by the worker threads. It could lead to the situation where the refcount is decremented below 0 and cause lots of problems. Presumably the !wb_has_dirty_io case is not a common one, so it can be discovered when the thread wakes up to check? Also add a comment in bdi_work_clear. Signed-off-by: Nick Piggin Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 7eba7326b9b9..8e1e5e19d21e 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -97,6 +97,11 @@ static void bdi_work_clear(struct bdi_work *work) { clear_bit(WS_USED_B, &work->state); smp_mb__after_clear_bit(); + /* + * work can have disappeared at this point. bit waitq functions + * should be able to tolerate this, provided bdi_sched_wait does + * not dereference it's pointer argument. + */ wake_up_bit(&work->state, WS_USED_B); } @@ -169,13 +174,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work) else { struct bdi_writeback *wb = &bdi->wb; - /* - * End work now if this wb has no dirty IO pending. Otherwise - * wakeup the handling thread - */ - if (!wb_has_dirty_io(wb)) - wb_clear_pending(wb, work); - else if (wb->task) + if (wb->task) wake_up_process(wb->task); } } -- 2.30.2