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>
---
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 2091db8..85f5c85 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -58,17 +58,24 @@ 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);
}
/* Kill _all_ buffers and pagecache , dirty or not.. */
--
1.8.1.4
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