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Subject[PATCH 002/106] writeback: Fix periodic writeback after fs mount
Date -stable review patch.  If anyone has any objections, please let me know.


From: Jan Kara <>

commit a5faeaf9109578e65e1a32e2a3e76c8b47e7dcb6 upstream.

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 <>
Signed-off-by: Jan Kara <>
Signed-off-by: Jens Axboe <>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <>
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 1244094..7da78cf 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 */
bdi_lock_two(&old->wb, &dst->wb);
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);
+ }
+ if (wakeup_bdi)
+ bdi_wakeup_thread_delayed(dst);

sector_t blkdev_max_block(struct block_device *bdev)

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