loop: Push loop_ctl_mutex down into loop_clr_fd()

loop_clr_fd() has a weird locking convention that is expects
loop_ctl_mutex held, releases it on success and keeps it on failure.
Untangle the mess by moving locking of loop_ctl_mutex into
loop_clr_fd().

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index eb01a685da4e0737bdbae9a42ee3cf6466bd9fa1..d8a7b5da881b62e6f1eae384140cdbff561bab73 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1027,15 +1027,22 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
 
 static int __loop_clr_fd(struct loop_device *lo)
 {
-       struct file *filp = lo->lo_backing_file;
+       struct file *filp = NULL;
        gfp_t gfp = lo->old_gfp_mask;
        struct block_device *bdev = lo->lo_device;
+       int err = 0;
 
-       if (WARN_ON_ONCE(lo->lo_state != Lo_rundown))
-               return -ENXIO;
+       mutex_lock(&loop_ctl_mutex);
+       if (WARN_ON_ONCE(lo->lo_state != Lo_rundown)) {
+               err = -ENXIO;
+               goto out_unlock;
+       }
 
-       if (filp == NULL)
-               return -EINVAL;
+       filp = lo->lo_backing_file;
+       if (filp == NULL) {
+               err = -EINVAL;
+               goto out_unlock;
+       }
 
        /* freeze request queue during the transition */
        blk_mq_freeze_queue(lo->lo_queue);
@@ -1082,6 +1089,7 @@ static int __loop_clr_fd(struct loop_device *lo)
        if (!part_shift)
                lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
        loop_unprepare_queue(lo);
+out_unlock:
        mutex_unlock(&loop_ctl_mutex);
        /*
         * Need not hold loop_ctl_mutex to fput backing file.
@@ -1089,14 +1097,22 @@ static int __loop_clr_fd(struct loop_device *lo)
         * lock dependency possibility warning as fput can take
         * bd_mutex which is usually taken before loop_ctl_mutex.
         */
-       fput(filp);
-       return 0;
+       if (filp)
+               fput(filp);
+       return err;
 }
 
 static int loop_clr_fd(struct loop_device *lo)
 {
-       if (lo->lo_state != Lo_bound)
+       int err;
+
+       err = mutex_lock_killable_nested(&loop_ctl_mutex, 1);
+       if (err)
+               return err;
+       if (lo->lo_state != Lo_bound) {
+               mutex_unlock(&loop_ctl_mutex);
                return -ENXIO;
+       }
        /*
         * If we've explicitly asked to tear down the loop device,
         * and it has an elevated reference count, set it for auto-teardown when
@@ -1113,6 +1129,7 @@ static int loop_clr_fd(struct loop_device *lo)
                return 0;
        }
        lo->lo_state = Lo_rundown;
+       mutex_unlock(&loop_ctl_mutex);
 
        return __loop_clr_fd(lo);
 }
@@ -1447,14 +1464,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
                mutex_unlock(&loop_ctl_mutex);
                break;
        case LOOP_CLR_FD:
-               err = mutex_lock_killable_nested(&loop_ctl_mutex, 1);
-               if (err)
-                       return err;
-               /* loop_clr_fd would have unlocked loop_ctl_mutex on success */
-               err = loop_clr_fd(lo);
-               if (err)
-                       mutex_unlock(&loop_ctl_mutex);
-               break;
+               return loop_clr_fd(lo);
        case LOOP_SET_STATUS:
                err = -EPERM;
                if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
@@ -1690,7 +1700,6 @@ out:
 static void lo_release(struct gendisk *disk, fmode_t mode)
 {
        struct loop_device *lo;
-       int err;
 
        mutex_lock(&loop_ctl_mutex);
        lo = disk->private_data;
@@ -1701,13 +1710,13 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
                if (lo->lo_state != Lo_bound)
                        goto out_unlock;
                lo->lo_state = Lo_rundown;
+               mutex_unlock(&loop_ctl_mutex);
                /*
                 * In autoclear mode, stop the loop thread
                 * and remove configuration after last close.
                 */
-               err = __loop_clr_fd(lo);
-               if (!err)
-                       return;
+               __loop_clr_fd(lo);
+               return;
        } else if (lo->lo_state == Lo_bound) {
                /*
                 * Otherwise keep thread (if running) and config,