linux-kernel - [PATCH 106/145] writeback: Fix periodic writeback after fs mount

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Message-Id: <1374101277-7915-107-git-send-email-kamal@canonical.com>
Date:	Wed, 17 Jul 2013 15:47:18 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 106/145] writeback: Fix periodic writeback after fs mount

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

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

From: Jan Kara <jack@...e.cz>

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 <Bert.DeJonghe@...lidata.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 883dc49..33f984f 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);
 }
 
 /* Kill _all_ buffers and pagecache , dirty or not.. */
-- 
1.8.1.2

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