linux-kernel - [ 38/77] block: fix synchronization and limit check in blk_alloc

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Date:	Fri,  1 Mar 2013 11:44:23 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 38/77] block: fix synchronization and limit check in blk_alloc_devt()

3.8-stable review patch.  If anyone has any objections, please let me know.

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

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

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@...nel.org>
Acked-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/genhd.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- 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.
@@ -424,19 +424,16 @@ int blk_alloc_devt(struct hd_struct *par
 			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;
 }


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