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author | Ming Lei <ming.lei@canonical.com> | 2015-05-06 12:26:23 +0800 |
---|---|---|
committer | Jens Axboe <axboe@fb.com> | 2015-05-20 09:06:09 -0600 |
commit | f8933667953e8e61bb6104f5ca88e32e85656a93 (patch) | |
tree | 25f3b20d8c1d27ac856a43f6655d9604c524fa9e /drivers/block/loop.c | |
parent | b816d45fd56c57180b63a03412b9f898d5736c58 (diff) | |
download | linux-stable-f8933667953e8e61bb6104f5ca88e32e85656a93.tar.gz linux-stable-f8933667953e8e61bb6104f5ca88e32e85656a93.tar.bz2 linux-stable-f8933667953e8e61bb6104f5ca88e32e85656a93.zip |
block: loop: don't hold lo_ctl_mutex in lo_open
The lo_ctl_mutex is held for running all ioctl handlers, and
in some ioctl handlers, ioctl_by_bdev(BLKRRPART) is called for
rereading partitions, which requires bd_mutex.
So it is easy to cause failure because trylock(bd_mutex) may
fail inside blkdev_reread_part(), and follows the lock context:
blkid or other application:
->open()
->mutex_lock(bd_mutex)
->lo_open()
->mutex_lock(lo_ctl_mutex)
losetup(set fd ioctl):
->mutex_lock(lo_ctl_mutex)
->ioctl_by_bdev(BLKRRPART)
->trylock(bd_mutex)
This patch trys to eliminate the ABBA lock dependency by removing
lo_ctl_mutext in lo_open() with the following approach:
1) make lo_refcnt as atomic_t and avoid acquiring lo_ctl_mutex in lo_open():
- for open vs. add/del loop, no any problem because of loop_index_mutex
- freeze request queue during clr_fd, so I/O can't come until
clearing fd is completed, like the effect of holding lo_ctl_mutex
in lo_open
- both open() and release() have been serialized by bd_mutex already
2) don't hold lo_ctl_mutex for decreasing/checking lo_refcnt in
lo_release(), then lo_ctl_mutex is only required for the last release.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Jarod Wilson <jarod@redhat.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'drivers/block/loop.c')
-rw-r--r-- | drivers/block/loop.c | 21 |
1 files changed, 12 insertions, 9 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 1bee523aa349..b3e294e529ec 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -831,7 +831,7 @@ static int loop_clr_fd(struct loop_device *lo) * <dev>/do something like mkfs/losetup -d <dev> causing the losetup -d * command to fail with EBUSY. */ - if (lo->lo_refcnt > 1) { + if (atomic_read(&lo->lo_refcnt) > 1) { lo->lo_flags |= LO_FLAGS_AUTOCLEAR; mutex_unlock(&lo->lo_ctl_mutex); return 0; @@ -840,6 +840,9 @@ static int loop_clr_fd(struct loop_device *lo) if (filp == NULL) return -EINVAL; + /* freeze request queue during the transition */ + blk_mq_freeze_queue(lo->lo_queue); + spin_lock_irq(&lo->lo_lock); lo->lo_state = Lo_rundown; lo->lo_backing_file = NULL; @@ -871,6 +874,8 @@ static int loop_clr_fd(struct loop_device *lo) lo->lo_state = Lo_unbound; /* This is safe: open() is still holding a reference. */ module_put(THIS_MODULE); + blk_mq_unfreeze_queue(lo->lo_queue); + if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev) ioctl_by_bdev(bdev, BLKRRPART, 0); lo->lo_flags = 0; @@ -1330,9 +1335,7 @@ static int lo_open(struct block_device *bdev, fmode_t mode) goto out; } - mutex_lock(&lo->lo_ctl_mutex); - lo->lo_refcnt++; - mutex_unlock(&lo->lo_ctl_mutex); + atomic_inc(&lo->lo_refcnt); out: mutex_unlock(&loop_index_mutex); return err; @@ -1343,11 +1346,10 @@ static void lo_release(struct gendisk *disk, fmode_t mode) struct loop_device *lo = disk->private_data; int err; - mutex_lock(&lo->lo_ctl_mutex); - - if (--lo->lo_refcnt) - goto out; + if (atomic_dec_return(&lo->lo_refcnt)) + return; + mutex_lock(&lo->lo_ctl_mutex); if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { /* * In autoclear mode, stop the loop thread @@ -1601,6 +1603,7 @@ static int loop_add(struct loop_device **l, int i) disk->flags |= GENHD_FL_NO_PART_SCAN; disk->flags |= GENHD_FL_EXT_DEVT; mutex_init(&lo->lo_ctl_mutex); + atomic_set(&lo->lo_refcnt, 0); lo->lo_number = i; spin_lock_init(&lo->lo_lock); disk->major = LOOP_MAJOR; @@ -1718,7 +1721,7 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, mutex_unlock(&lo->lo_ctl_mutex); break; } - if (lo->lo_refcnt > 0) { + if (atomic_read(&lo->lo_refcnt) > 0) { ret = -EBUSY; mutex_unlock(&lo->lo_ctl_mutex); break; |