Commit a5faeaf9 authored Jun 28, 2013 by Jan Kara Committed by Jens Axboe Jun 28, 2013

writeback: Fix periodic writeback after fs mount

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@amplidata.com>
CC: stable@vger.kernel.org # >= 3.0
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 9138125b

fs/block_dev.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -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.. */

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