[PATCH V2] btrfs: close any open devices if btrfs_mount fails

[Eric Sandeen <sandeen@redhat.com>]

This:

   # mkfs.btrfs /dev/sdb{1,2} ; wipefs -a /dev/sdb1; mount /dev/sdb2 /mnt/test

would lead to a blkdev open/close mismatch when the mount fails, and
a permanently busy (opened O_EXCL) sdb2:

   # wipefs -a /dev/sdb2
   wipefs: error: /dev/sdb2: probing initialization failed: Device or resource busy

It's because btrfs_open_devices() may open some devices, and still
return failure.  So the error unwinding needs to close any open
devices in fs_devices before returning.

Reported-by: Jan Safranek <jsafrane@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

V2: use open_devices not opened, that seems like the right test...
if a test is necessary I'm not certain, tbh.  Seems prudently
defensive.

Note, __btrfs_open_devices is weird; it seems to return success or
failure based on the outcome of the result of the last call
to btrfs_get_bdev_and_sb().  But that's a different bug...

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f6b8859..60c67fa 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1125,7 +1125,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 
 	error = btrfs_open_devices(fs_devices, mode, fs_type);
 	if (error)
-		goto error_fs_info;
+		goto error_close_devices;
 
 	if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
 		error = -EACCES;
@@ -1161,7 +1161,8 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 	return root;
 
 error_close_devices:
-	btrfs_close_devices(fs_devices);
+	if (fs_devices->open_devices)
+		btrfs_close_devices(fs_devices);
 error_fs_info:
 	free_fs_info(fs_info);
 	return ERR_PTR(error);

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