linux-ext4 - [PATCH] ext4: queue conversion after adding to inode's completed IO list

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Message-ID: <4C5C67FD.5070208@redhat.com>
Date:	Fri, 06 Aug 2010 15:52:29 -0400
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
CC:	Jiaying Zhang <jiayingz@...gle.com>
Subject: [PATCH] ext4: queue conversion after adding to inode's completed
 IO list

By queuing the io end on the unwritten workqueue before adding it
to our inode's list of completed IOs, I think we run the risk
of the work getting completed, and the IO freed, before we try
to add it to the inode's i_completed_io_list.

It should be safe to add it to the inode's list of completed
IOs, and -then- queue it for completion, I think.

Thanks to Dave Chinner for pointing out the race.

Signed-off-by: Eric Sandeen <sandeen@...hat.com>
---

(At least I think this is right; I haven't actually demonstrated a race...)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0afc8c1..7f56c48 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3804,14 +3804,14 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
 	io_end->flag = EXT4_IO_UNWRITTEN;
 	wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
 
-	/* queue the work to convert unwritten extents to written */
-	queue_work(wq, &io_end->work);
-
 	/* Add the io_end to per-inode completed aio dio list*/
 	ei = EXT4_I(io_end->inode);
 	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
 	list_add_tail(&io_end->list, &ei->i_completed_io_list);
 	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
+
+	/* queue the work to convert unwritten extents to written */
+	queue_work(wq, &io_end->work);
 	iocb->private = NULL;
 out:
 	if (is_async)

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