Revert "block/loop: Use global lock for ioctl() operation."

BugLink: https://bugs.launchpad.net/bugs/1830176

This reverts commit b3f3107f which is
commit 310ca162 upstream.

Jan Kara has reported seeing problems with this patch applied, as has
Salvatore Bonaccorso, so let's drop it for now.
Reported-by: Salvatore Bonaccorso <carnil@debian.org>
Reported-by: Jan Kara <jack@suse.cz>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[juergh: Adjusted context.]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/block/loop.c

@@ -82,7 +82,6 @@
 
 static DEFINE_IDR(loop_index_idr);
 static DEFINE_MUTEX(loop_index_mutex);
-static DEFINE_MUTEX(loop_ctl_mutex);
 
 static int max_part;
 static int part_shift;
@@ -1098,7 +1097,7 @@ static int loop_clr_fd(struct loop_device *lo)
 	 */
 	if (atomic_read(&lo->lo_refcnt) > 1) {
 		lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
-		mutex_unlock(&loop_ctl_mutex);
+		mutex_unlock(&lo->lo_ctl_mutex);
 		return 0;
 	}
 
@@ -1148,12 +1147,12 @@ 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);
-	mutex_unlock(&loop_ctl_mutex);
+	mutex_unlock(&lo->lo_ctl_mutex);
 	/*
-	 * Need not hold loop_ctl_mutex to fput backing file.
-	 * Calling fput holding loop_ctl_mutex triggers a circular
+	 * Need not hold lo_ctl_mutex to fput backing file.
+	 * Calling fput holding lo_ctl_mutex triggers a circular
 	 * lock dependency possibility warning as fput can take
-	 * bd_mutex which is usually taken before loop_ctl_mutex.
+	 * bd_mutex which is usually taken before lo_ctl_mutex.
 	 */
 	fput(filp);
 	if (virt_filp)
@@ -1418,7 +1417,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 	struct loop_device *lo = bdev->bd_disk->private_data;
 	int err;
 
-	mutex_lock_nested(&loop_ctl_mutex, 1);
+	mutex_lock_nested(&lo->lo_ctl_mutex, 1);
 	switch (cmd) {
 	case LOOP_SET_FD:
 		err = loop_set_fd(lo, mode, bdev, arg);
@@ -1427,7 +1426,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 		err = loop_change_fd(lo, bdev, arg);
 		break;
 	case LOOP_CLR_FD:
-		/* loop_clr_fd would have unlocked loop_ctl_mutex on success */
+		/* loop_clr_fd would have unlocked lo_ctl_mutex on success */
 		err = loop_clr_fd(lo);
 		if (!err)
 			goto out_unlocked;
@@ -1463,7 +1462,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 	default:
 		err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
 	}
-	mutex_unlock(&loop_ctl_mutex);
+	mutex_unlock(&lo->lo_ctl_mutex);
 
 out_unlocked:
 	return err;
@@ -1596,16 +1595,16 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
 
 	switch(cmd) {
 	case LOOP_SET_STATUS:
-		mutex_lock(&loop_ctl_mutex);
+		mutex_lock(&lo->lo_ctl_mutex);
 		err = loop_set_status_compat(
 			lo, (const struct compat_loop_info __user *) arg);
-		mutex_unlock(&loop_ctl_mutex);
+		mutex_unlock(&lo->lo_ctl_mutex);
 		break;
 	case LOOP_GET_STATUS:
-		mutex_lock(&loop_ctl_mutex);
+		mutex_lock(&lo->lo_ctl_mutex);
 		err = loop_get_status_compat(
 			lo, (struct compat_loop_info __user *) arg);
-		mutex_unlock(&loop_ctl_mutex);
+		mutex_unlock(&lo->lo_ctl_mutex);
 		break;
 	case LOOP_SET_CAPACITY:
 	case LOOP_CLR_FD:
@@ -1649,7 +1648,7 @@ static void __lo_release(struct loop_device *lo)
 	if (atomic_dec_return(&lo->lo_refcnt))
 		return;
 
-	mutex_lock(&loop_ctl_mutex);
+	mutex_lock(&lo->lo_ctl_mutex);
 	if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
 		/*
 		 * In autoclear mode, stop the loop thread
@@ -1666,7 +1665,7 @@ static void __lo_release(struct loop_device *lo)
 		loop_flush(lo);
 	}
 
-	mutex_unlock(&loop_ctl_mutex);
+	mutex_unlock(&lo->lo_ctl_mutex);
 }
 
 static void lo_release(struct gendisk *disk, fmode_t mode)
@@ -1712,10 +1711,10 @@ static int unregister_transfer_cb(int id, void *ptr, void *data)
 	struct loop_device *lo = ptr;
 	struct loop_func_table *xfer = data;
 
-	mutex_lock(&loop_ctl_mutex);
+	mutex_lock(&lo->lo_ctl_mutex);
 	if (lo->lo_encryption == xfer)
 		loop_release_xfer(lo);
-	mutex_unlock(&loop_ctl_mutex);
+	mutex_unlock(&lo->lo_ctl_mutex);
 	return 0;
 }
 
@@ -1877,6 +1876,7 @@ static int loop_add(struct loop_device **l, int i)
 	if (!part_shift)
 		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);
@@ -1989,19 +1989,19 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
 		ret = loop_lookup(&lo, parm);
 		if (ret < 0)
 			break;
-		mutex_lock(&loop_ctl_mutex);
+		mutex_lock(&lo->lo_ctl_mutex);
 		if (lo->lo_state != Lo_unbound) {
 			ret = -EBUSY;
-			mutex_unlock(&loop_ctl_mutex);
+			mutex_unlock(&lo->lo_ctl_mutex);
 			break;
 		}
 		if (atomic_read(&lo->lo_refcnt) > 0) {
 			ret = -EBUSY;
-			mutex_unlock(&loop_ctl_mutex);
+			mutex_unlock(&lo->lo_ctl_mutex);
 			break;
 		}
 		lo->lo_disk->private_data = NULL;
-		mutex_unlock(&loop_ctl_mutex);
+		mutex_unlock(&lo->lo_ctl_mutex);
 		idr_remove(&loop_index_idr, lo->lo_number);
 		loop_remove(lo);
 		break;

drivers/block/loop.h

@@ -55,6 +55,7 @@ struct loop_device {
 
 	spinlock_t		lo_lock;
 	int			lo_state;
+	struct mutex		lo_ctl_mutex;
 	struct kthread_worker	worker;
 	struct task_struct	*worker_task;
 	bool			use_dio;