Re: Loopback device hung [was Re: xfs deadlock on 3.9-rc5 running xfstests case #78]

From: Phillip Susi <psusi@ubuntu.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: CAI Qian <caiqian@redhat.com>, Dave Chinner <david@fromorbit.com>,
	xfs@oss.sgi.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Loopback device hung [was Re: xfs deadlock on 3.9-rc5 running xfstests case #78]
Date: Thu, 04 Apr 2013 16:30:54 -0400	[thread overview]
Message-ID: <515DE2FE.1080201@ubuntu.com> (raw)
In-Reply-To: <515C4D9D.10103@ubuntu.com>


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> I have not tested it yet, but I am pretty sure it won't work.  It
> looks like the patch changes the BLKRRPART path to go ahead and remove
> existing partitions when GENHD_FL_NO_PARTSCAN is set.  loop doesn't
> issue the BLKRRPART ioctl when !LO_FLAGS_PARTSCAN so this won't help.
>  I think loop needs to set GENHD_FL_NO_PARTSCAN and then issue the
> ioctl regardless of the LO_FLAGS_PARTSCAN flag to get the partitions
> to be removed.  I will try to test tonight.

After testing, my initial thoughts appeared to have been correct.  I had
to modify the patch as follows.  To test, simply do:

truncate -s 10m img
losetup /dev/loop0 img
parted /dev/loop0
mklabel msdos
mkpart primary ext2 1m 2m
quit
ls /dev/loop0*

Note the /dev/loop0p1 node.  Run losetup -d /dev/loop0 and see if it is
still there.



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diff --git a/block/ioctl.c b/block/ioctl.c
index a31d91d..8b78b5a 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -155,7 +155,7 @@ static int blkdev_reread_part(struct block_device *bdev)
 	struct gendisk *disk = bdev->bd_disk;
 	int res;
 
-	if (!disk_part_scan_enabled(disk) || bdev != bdev->bd_contains)
+	if (bdev != bdev->bd_contains)
 		return -EINVAL;
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 1cb4dec..0e7d637 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -430,6 +430,15 @@ rescan:
 		disk->fops->revalidate_disk(disk);
 	check_disk_size_change(disk, bdev);
 	bdev->bd_invalidated = 0;
+
+	/*
+	 * If partition scanning is disabled, we are done.
+	 */
+	if (!disk_part_scan_enabled(disk)) {
+		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
+		return 0;
+	}
+
 	if (!get_capacity(disk) || !(state = check_partition(disk, bdev)))
 		return 0;
 	if (IS_ERR(state)) {
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 8bc6d39..326fac9 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1039,11 +1039,9 @@ static int loop_clr_fd(struct loop_device *lo)
 	lo->lo_state = Lo_unbound;
 	/* This is safe: open() is still holding a reference. */
 	module_put(THIS_MODULE);
-	if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
-		ioctl_by_bdev(bdev, BLKRRPART, 0);
+	lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
+	ioctl_by_bdev(bdev, BLKRRPART, 0);
 	lo->lo_flags = 0;
-	if (!part_shift)
-		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
 	mutex_unlock(&lo->lo_ctl_mutex);
 	/*
 	 * Need not hold lo_ctl_mutex to fput backing file.


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