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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@kernel.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@kernel.org>
Reported-by: Alex Villacis Lasso <avillaci@ceibo.fiec.espol.edu.ec>
Tested-by: Alex Villacis Lasso <avillaci@ceibo.fiec.espol.edu.ec>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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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