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authorJan Kara <jack@suse.cz>2019-07-30 13:10:14 +0200
committerJens Axboe <axboe@kernel.dk>2019-07-30 13:16:57 -0600
commit89e524c04fa966330e2e80ab2bc50b9944c5847a (patch)
treeb384005acf4d525150d0a8eb0d7a62b33a44e798 /include/linux
parent71d6c505b4d9e6f76586350450e785e3d452b346 (diff)
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 'include/linux')
-rw-r--r--include/linux/fs.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 56b8e358af5c..997a530ff4e9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2598,6 +2598,12 @@ extern struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
void *holder);
extern struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode,
void *holder);
+extern struct block_device *bd_start_claiming(struct block_device *bdev,
+ void *holder);
+extern void bd_finish_claiming(struct block_device *bdev,
+ struct block_device *whole, void *holder);
+extern void bd_abort_claiming(struct block_device *bdev,
+ struct block_device *whole, void *holder);
extern void blkdev_put(struct block_device *bdev, fmode_t mode);
extern int __blkdev_reread_part(struct block_device *bdev);
extern int blkdev_reread_part(struct block_device *bdev);