[037/251] writeback: Fix periodic writeback after fs mount

[Steven Rostedt]

3.6.11.9-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@xxxxxxx>

[ Upstream commit a5faeaf9109578e65e1a32e2a3e76c8b47e7dcb6 ]

Code in blkdev.c moves a device inode to default_backing_dev_info when
the last reference to the device is put and moves the device inode back
to its bdi when the first reference is acquired. This includes moving to
wb.b_dirty list if the device inode is dirty. The code however doesn't
setup timer to wake corresponding flusher thread and while wb.b_dirty
list is non-empty __mark_inode_dirty() will not set it up either. Thus
periodic writeback is effectively disabled until a sync(2) call which can
lead to unexpected data loss in case of crash or power failure.

Fix the problem by setting up a timer for periodic writeback in case we
add the first dirty inode to wb.b_dirty list in bdev_inode_switch_bdi().

Reported-by: Bert De Jonghe <Bert.DeJonghe@xxxxxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx # >= 3.0
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 fs/block_dev.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index daaca3d..41f6594 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -57,17 +57,24 @@ static void bdev_inode_switch_bdi(struct inode *inode,
 			struct backing_dev_info *dst)
 {
 	struct backing_dev_info *old = inode->i_data.backing_dev_info;
+	bool wakeup_bdi = false;
 
 	if (unlikely(dst == old))		/* deadlock avoidance */
 		return;
 	bdi_lock_two(&old->wb, &dst->wb);
 	spin_lock(&inode->i_lock);
 	inode->i_data.backing_dev_info = dst;
-	if (inode->i_state & I_DIRTY)
+	if (inode->i_state & I_DIRTY) {
+		if (bdi_cap_writeback_dirty(dst) && !wb_has_dirty_io(&dst->wb))
+			wakeup_bdi = true;
 		list_move(&inode->i_wb_list, &dst->wb.b_dirty);
+	}
 	spin_unlock(&inode->i_lock);
 	spin_unlock(&old->wb.list_lock);
 	spin_unlock(&dst->wb.list_lock);
+
+	if (wakeup_bdi)
+		bdi_wakeup_thread_delayed(dst);
 }
 
 sector_t blkdev_max_block(struct block_device *bdev)
-- 
1.7.10.4


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