linux-kernel - [PATCH 012/106] dm mpath: fix ioctl deadlock when no paths

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Message-Id: <1375176725-5825-13-git-send-email-luis.henriques@canonical.com>
Date:	Tue, 30 Jul 2013 10:30:31 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Hannes Reinecke <hare@...e.de>, Mike Snitzer <snitzer@...hat.com>,
	Alasdair G Kergon <agk@...hat.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 012/106] dm mpath: fix ioctl deadlock when no paths

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

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

From: Hannes Reinecke <hare@...e.de>

commit 6c182cd88d179cbbd06f4f8a8a19b6977940753f upstream.

When multipath needs to retry an ioctl the reference to the
current live table needs to be dropped. Otherwise a deadlock
occurs when all paths are down:
- dm_blk_ioctl takes a reference to the current table
  and spins in multipath_ioctl().
- A new table is being loaded, but upon resume the process
  hangs in dm_table_destroy() waiting for references to
  drop to zero.

With this patch the reference to the old table is dropped
prior to retry, thereby avoiding the deadlock.

Signed-off-by: Hannes Reinecke <hare@...e.de>
Cc: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Alasdair G Kergon <agk@...hat.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/md/dm-mpath.c | 8 ++------
 drivers/md/dm.c       | 9 ++++++++-
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 1ca41d2..93b3c2d 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1526,7 +1526,6 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
 	unsigned long flags;
 	int r;
 
-again:
 	bdev = NULL;
 	mode = 0;
 	r = 0;
@@ -1544,7 +1543,7 @@ again:
 	}
 
 	if ((pgpath && m->queue_io) || (!pgpath && m->queue_if_no_path))
-		r = -EAGAIN;
+		r = -ENOTCONN;
 	else if (!bdev)
 		r = -EIO;
 
@@ -1556,11 +1555,8 @@ again:
 	if (!r && ti->len != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT)
 		r = scsi_verify_blk_ioctl(NULL, cmd);
 
-	if (r == -EAGAIN && !fatal_signal_pending(current)) {
+	if (r == -ENOTCONN && !fatal_signal_pending(current))
 		queue_work(kmultipathd, &m->process_queued_ios);
-		msleep(10);
-		goto again;
-	}
 
 	return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);
 }
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 32370ea..9a7290b 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -414,10 +414,12 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
 			unsigned int cmd, unsigned long arg)
 {
 	struct mapped_device *md = bdev->bd_disk->private_data;
-	struct dm_table *map = dm_get_live_table(md);
+	struct dm_table *map;
 	struct dm_target *tgt;
 	int r = -ENOTTY;
 
+retry:
+	map = dm_get_live_table(md);
 	if (!map || !dm_table_get_size(map))
 		goto out;
 
@@ -438,6 +440,11 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
 out:
 	dm_table_put(map);
 
+	if (r == -ENOTCONN) {
+		msleep(10);
+		goto retry;
+	}
+
 	return r;
 }
 
-- 
1.8.3.2

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