linux-kernel - [PATCH 3/7] block: loop: fix another reread part failure

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Date:	Wed,  8 Apr 2015 02:23:42 -0400
From:	Jarod Wilson <jarod@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Jarod Wilson <jarod@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Markus Pargmann <mpa@...gutronix.de>,
	Stefan Weinhuber <wein@...ibm.com>,
	Stefan Haberland <stefan.haberland@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Fabian Frederick <fabf@...net.be>,
	Ming Lei <ming.lei@...onical.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	nbd-general@...ts.sourceforge.net, linux-s390@...r.kernel.org
Subject: [PATCH 3/7] block: loop: fix another reread part failure

loop_clr_fd() can be run piggyback with lo_release(), and
under this situation, reread partition may always fail because
of bd_mutex which has been held in release path.

This patch detects the situation by the reference count, and
call blkdev_reread_part_nolock() to avoid acquiring the lock again.

In the meantime, this patch switches to new kernel APIs
of blkdev_reread_part() and blkdev_reread_part_nolock().

[jarod: this is a merger of my original patch, Ming's patch, and some
reworking for my reworked first patch in the series.]

CC: Christoph Hellwig <hch@...radead.org>
CC: Jens Axboe <axboe@...nel.dk>
CC: Tejun Heo <tj@...nel.org>
CC: Alexander Viro <viro@...iv.linux.org.uk>
CC: Markus Pargmann <mpa@...gutronix.de>
CC: Stefan Weinhuber <wein@...ibm.com>
CC: Stefan Haberland <stefan.haberland@...ibm.com>
CC: Sebastian Ott <sebott@...ux.vnet.ibm.com>
CC: Fabian Frederick <fabf@...net.be>
CC: Ming Lei <ming.lei@...onical.com>
CC: David Herrmann <dh.herrmann@...il.com>
CC: Mike Galbraith <bitbucket@...ine.de>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: nbd-general@...ts.sourceforge.net
CC: linux-s390@...r.kernel.org
Signed-off-by: Jarod Wilson <jarod@...hat.com>
---
 drivers/block/loop.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 81a6bc1..ab5c678 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -528,6 +528,26 @@ static int loop_flush(struct loop_device *lo)
 	return loop_switch(lo, NULL);
 }
 
+static void loop_reread_partitions(struct loop_device *lo,
+				   struct block_device *bdev)
+{
+	int rc;
+	bool in_release;
+
+	mutex_lock(&lo->lo_open_mutex);
+	in_release = lo->lo_refcnt == 0;
+	mutex_unlock(&lo->lo_open_mutex);
+
+	/* bd_mutex has been held already in release path */
+	if (in_release)
+		rc = __blkdev_reread_part(bdev);
+	else
+		rc = blkdev_reread_part(bdev);
+	if (rc)
+		pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
+			__func__, lo->lo_number, lo->lo_file_name, rc);
+}
+
 /*
  * loop_change_fd switched the backing store of a loopback device to
  * a new file. This is useful for operating system installers to free up
@@ -576,7 +596,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 
 	fput(old_file);
 	if (lo->lo_flags & LO_FLAGS_PARTSCAN)
-		ioctl_by_bdev(bdev, BLKRRPART, 0);
+		loop_reread_partitions(lo, bdev);
 	return 0;
 
  out_putf:
@@ -807,7 +827,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	if (part_shift)
 		lo->lo_flags |= LO_FLAGS_PARTSCAN;
 	if (lo->lo_flags & LO_FLAGS_PARTSCAN)
-		ioctl_by_bdev(bdev, BLKRRPART, 0);
+		loop_reread_partitions(lo, bdev);
 
 	/* Grab the block_device to prevent its destruction after we
 	 * put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev).
@@ -933,7 +953,7 @@ static int loop_clr_fd(struct loop_device *lo)
 	mutex_unlock(&lo->lo_open_mutex);
 
 	if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
-		ioctl_by_bdev(bdev, BLKRRPART, 0);
+		loop_reread_partitions(lo, bdev);
 	lo->lo_flags = 0;
 	if (!part_shift)
 		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
@@ -1008,7 +1028,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 	     !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
 		lo->lo_flags |= LO_FLAGS_PARTSCAN;
 		lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
-		ioctl_by_bdev(lo->lo_device, BLKRRPART, 0);
+		loop_reread_partitions(lo, lo->lo_device);
 	}
 
 	lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
-- 
1.8.3.1

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