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Subject[PATCH] mm: fix refcounting in swapon
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From: Miklos Szeredi <mszeredi@suse.cz>

Grab a reference to bdev before calling blkdev_get(), which expects
the refcount to be already incremented and either returns success or
decrements the refcount and returns an error.

The bug was introduced by e525fd89 (block: make blkdev_get/put()
handle exclusive access), which didn't take into account this behavior
of blkdev_get().

CC: Tejun Heo <tj@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
mm/swapfile.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux.git/mm/swapfile.c
===================================================================
--- linux.git.orig/mm/swapfile.c 2011-02-24 15:29:26.000000000 +0100
+++ linux.git/mm/swapfile.c 2011-02-24 15:32:31.000000000 +0100
@@ -1940,7 +1940,7 @@ SYSCALL_DEFINE2(swapon, const char __use

error = -EINVAL;
if (S_ISBLK(inode->i_mode)) {
- bdev = I_BDEV(inode);
+ bdev = bdgrab(I_BDEV(inode));
error = blkdev_get(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL,
sys_swapon);
if (error < 0) {

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