linux-kernel - [077/107] block: use the passed in @bdev when claiming if partno is zero

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Date:	Thu, 07 Jul 2011 17:16:49 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Tejun Heo <tj@...nel.org>, Jens Axboe <jaxboe@...ionio.com>
Subject: [077/107] block: use the passed in @bdev when claiming if partno is zero

2.6.39-stable review patch.  If anyone has any objections, please let us know.

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

From: Tejun Heo <tj@...nel.org>

commit d4c208b86b8be4254eba0e74071496e599f94639 upstream.

6b4517a791 (block: implement bd_claiming and claiming block)
introduced claiming block to support O_EXCL blkdev opens properly.

bd_start_claiming() looks up the part 0 bdev and starts claiming
block.  The function assumed that there is only one part 0 bdev and
always used bdget_disk(disk, 0) to look it up; unfortunately, this
isn't true for some drivers (floppy) which use multiple block devices
to denote different operating parameters for the same physical device.
There can be multiple part 0 bdev's for the same device number.

This incorrect assumption caused the wrong bdev to be used during
claiming leading to unbalanced bd_holders as reported in the following
bug.

  https://bugzilla.kernel.org/show_bug.cgi?id=28522

This patch updates bd_start_claiming() such that it uses the bdev
specified as argument if its partno is zero.

Note that this means that different bdev's can be used for the same
device and O_EXCL check can be effectively bypassed.  It has always
been broken that way and floppy is fortunately on its way out.  Leave
that breakage alone.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Alex Villacis Lasso <avillaci@...bo.fiec.espol.edu.ec>
Tested-by: Alex Villacis Lasso <avillaci@...bo.fiec.espol.edu.ec>
Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/block_dev.c |   14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -762,7 +762,19 @@ static struct block_device *bd_start_cla
 	if (!disk)
 		return ERR_PTR(-ENXIO);

-	whole = bdget_disk(disk, 0);
+	/*
+	 * Normally, @bdev should equal what's returned from bdget_disk()
+	 * if partno is 0; however, some drivers (floppy) use multiple
+	 * bdev's for the same physical device and @bdev may be one of the
+	 * aliases.  Keep @bdev if partno is 0.  This means claimer
+	 * tracking is broken for those devices but it has always been that
+	 * way.
+	 */
+	if (partno)
+		whole = bdget_disk(disk, 0);
+	else
+		whole = bdgrab(bdev);
+
 	module_put(disk->fops->owner);
 	put_disk(disk);
 	if (!whole)

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