[ 3.5.y.z extended stable ] Patch "block: fix synchronization and limit check in" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    block: fix synchronization and limit check in

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 5053becfa2c0e11a4c9bf0566c5459966121aac9 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj at kernel.org>
Date: Wed, 27 Feb 2013 17:03:56 -0800
Subject: [PATCH] block: fix synchronization and limit check in
 blk_alloc_devt()

commit ce23bba842aee98092225d9576dba47c82352521 upstream.

idr allocation in blk_alloc_devt() wasn't synchronized against lookup
and removal, and its limit check was off by one - 1 << MINORBITS is
the number of minors allowed, not the maximum allowed minor.

Add locking and rename MAX_EXT_DEVT to NR_EXT_DEVT and fix limit
checking.

Signed-off-by: Tejun Heo <tj at kernel.org>
Acked-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 block/genhd.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 9433636..60108d9 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -25,7 +25,7 @@ static DEFINE_MUTEX(block_class_lock);
 struct kobject *block_depr;

 /* for extended dynamic devt allocation, currently only one major is used */
-#define MAX_EXT_DEVT		(1 << MINORBITS)
+#define NR_EXT_DEVT		(1 << MINORBITS)

 /* For extended devt allocation.  ext_devt_mutex prevents look up
  * results from going away underneath its user.
@@ -422,19 +422,16 @@ int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
 			return -ENOMEM;
 		mutex_lock(&ext_devt_mutex);
 		rc = idr_get_new(&ext_devt_idr, part, &idx);
+		if (!rc && idx >= NR_EXT_DEVT) {
+			idr_remove(&ext_devt_idr, idx);
+			rc = -EBUSY;
+		}
 		mutex_unlock(&ext_devt_mutex);
 	} while (rc == -EAGAIN);

 	if (rc)
 		return rc;

-	if (idx > MAX_EXT_DEVT) {
-		mutex_lock(&ext_devt_mutex);
-		idr_remove(&ext_devt_idr, idx);
-		mutex_unlock(&ext_devt_mutex);
-		return -EBUSY;
-	}
-
 	*devt = MKDEV(BLOCK_EXT_MAJOR, blk_mangle_minor(idx));
 	return 0;
 }
--
1.8.1.2