From 146d7009b45cdb45ec3be8ad73177dae58f4bc91 Mon Sep 17 00:00:00 2001 From: Junxiao Bi Date: Wed, 11 Sep 2013 14:23:04 -0700 Subject: [PATCH] writeback: fix race that cause writeback hung There is a race between mark inode dirty and writeback thread, see the following scenario. In this case, writeback thread will not run though there is dirty_io. __mark_inode_dirty() bdi_writeback_workfn() ... ... spin_lock(&inode->i_lock); ... if (bdi_cap_writeback_dirty(bdi)) { <<< assume wb has dirty_io, so wakeup_bdi is false. <<< the following inode_dirty also have wakeup_bdi false. if (!wb_has_dirty_io(&bdi->wb)) wakeup_bdi = true; } spin_unlock(&inode->i_lock); <<< assume last dirty_io is removed here. pages_written = wb_do_writeback(wb); ... <<< work_list empty and wb has no dirty_io, <<< delayed_work will not be queued. if (!list_empty(&bdi->work_list) || (wb_has_dirty_io(wb) && dirty_writeback_interval)) queue_delayed_work(bdi_wq, &wb->dwork, msecs_to_jiffies(dirty_writeback_interval * 10)); spin_lock(&bdi->wb.list_lock); inode->dirtied_when = jiffies; <<< new dirty_io is added. list_move(&inode->i_wb_list, &bdi->wb.b_dirty); spin_unlock(&bdi->wb.list_lock); <<< though there is dirty_io, but wakeup_bdi is false, <<< so writeback thread will not be waked up and <<< the new dirty_io will not be flushed. if (wakeup_bdi) bdi_wakeup_thread_delayed(bdi); Writeback will run until there is a new flush work queued. This may cause a lot of dirty pages stay in memory for a long time. Signed-off-by: Junxiao Bi Reviewed-by: Jan Kara Cc: Fengguang Wu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/fs-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 54b3c31c2f0d..30f6f27d5a59 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1171,6 +1171,8 @@ void __mark_inode_dirty(struct inode *inode, int flags) bool wakeup_bdi = false; bdi = inode_to_bdi(inode); + spin_unlock(&inode->i_lock); + spin_lock(&bdi->wb.list_lock); if (bdi_cap_writeback_dirty(bdi)) { WARN(!test_bit(BDI_registered, &bdi->state), "bdi-%s not registered\n", bdi->name); @@ -1185,8 +1187,6 @@ void __mark_inode_dirty(struct inode *inode, int flags) wakeup_bdi = true; } - spin_unlock(&inode->i_lock); - spin_lock(&bdi->wb.list_lock); inode->dirtied_when = jiffies; list_move(&inode->i_wb_list, &bdi->wb.b_dirty); spin_unlock(&bdi->wb.list_lock); -- 2.20.1