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authorJan Kara <jack@suse.cz>2019-07-30 14:10:14 +0300
committerJens Axboe <axboe@kernel.dk>2019-07-30 22:16:57 +0300
commit89e524c04fa966330e2e80ab2bc50b9944c5847a (patch)
treeb384005acf4d525150d0a8eb0d7a62b33a44e798 /drivers/block/loop.c
parent71d6c505b4d9e6f76586350450e785e3d452b346 (diff)
downloadlinux-89e524c04fa966330e2e80ab2bc50b9944c5847a.tar.xz
loop: Fix mount(2) failure due to race with LOOP_SET_FD
Commit 33ec3e53e7b1 ("loop: Don't change loop device under exclusive opener") made LOOP_SET_FD ioctl acquire exclusive block device reference while it updates loop device binding. However this can make perfectly valid mount(2) fail with EBUSY due to racing LOOP_SET_FD holding temporarily the exclusive bdev reference in cases like this: for i in {a..z}{a..z}; do dd if=/dev/zero of=$i.image bs=1k count=0 seek=1024 mkfs.ext2 $i.image mkdir mnt$i done echo "Run" for i in {a..z}{a..z}; do mount -o loop -t ext2 $i.image mnt$i & done Fix the problem by not getting full exclusive bdev reference in LOOP_SET_FD but instead just mark the bdev as being claimed while we update the binding information. This just blocks new exclusive openers instead of failing them with EBUSY thus fixing the problem. Fixes: 33ec3e53e7b1 ("loop: Don't change loop device under exclusive opener") Cc: stable@vger.kernel.org Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block/loop.c')
-rw-r--r--drivers/block/loop.c16
1 files changed, 9 insertions, 7 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 44c9985f352a..3036883fc9f8 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -924,6 +924,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
struct file *file;
struct inode *inode;
struct address_space *mapping;
+ struct block_device *claimed_bdev = NULL;
int lo_flags = 0;
int error;
loff_t size;
@@ -942,10 +943,11 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
* here to avoid changing device under exclusive owner.
*/
if (!(mode & FMODE_EXCL)) {
- bdgrab(bdev);
- error = blkdev_get(bdev, mode | FMODE_EXCL, loop_set_fd);
- if (error)
+ claimed_bdev = bd_start_claiming(bdev, loop_set_fd);
+ if (IS_ERR(claimed_bdev)) {
+ error = PTR_ERR(claimed_bdev);
goto out_putf;
+ }
}
error = mutex_lock_killable(&loop_ctl_mutex);
@@ -1015,15 +1017,15 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
mutex_unlock(&loop_ctl_mutex);
if (partscan)
loop_reread_partitions(lo, bdev);
- if (!(mode & FMODE_EXCL))
- blkdev_put(bdev, mode | FMODE_EXCL);
+ if (claimed_bdev)
+ bd_abort_claiming(bdev, claimed_bdev, loop_set_fd);
return 0;
out_unlock:
mutex_unlock(&loop_ctl_mutex);
out_bdev:
- if (!(mode & FMODE_EXCL))
- blkdev_put(bdev, mode | FMODE_EXCL);
+ if (claimed_bdev)
+ bd_abort_claiming(bdev, claimed_bdev, loop_set_fd);
out_putf:
fput(file);
out: