btrfs: update device path inode time instead of bd_inode

Christoph pointed out that I'm updating bdev->bd_inode for the device
time when we remove block devices from a btrfs file system, however this
isn't actually exposed to anything.  The inode we want to update is the
one that's associated with the path to the device, usually on devtmpfs,
so that blkid notices the difference.

We still don't want to do the blkdev_open, so use kern_path() to get the
path to the given device and do the update time on that inode.

Fixes: 8f96a5bfa150 ("btrfs: update the bdev time directly when closing")
Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 9eab8a7411665cb6e7d69f68824b4296f64ee1f5..a8ea3f88c4dbdfac9302255d641ca9be0fecb6e6 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -14,6 +14,7 @@
 #include <linux/semaphore.h>
 #include <linux/uuid.h>
 #include <linux/list_sort.h>
+#include <linux/namei.h>
 #include "misc.h"
 #include "ctree.h"
 #include "extent_map.h"
@@ -1888,18 +1889,22 @@ out:
 /*
  * Function to update ctime/mtime for a given device path.
  * Mainly used for ctime/mtime based probe like libblkid.
+ *
+ * We don't care about errors here, this is just to be kind to userspace.
  */
-static void update_dev_time(struct block_device *bdev)
+static void update_dev_time(const char *device_path)
 {
-       struct inode *inode = bdev->bd_inode;
+       struct path path;
        struct timespec64 now;
+       int ret;
 
-       /* Shouldn't happen but just in case. */
-       if (!inode)
+       ret = kern_path(device_path, LOOKUP_FOLLOW, &path);
+       if (ret)
                return;
 
-       now = current_time(inode);
-       generic_update_time(inode, &now, S_MTIME | S_CTIME);
+       now = current_time(d_inode(path.dentry));
+       inode_update_time(d_inode(path.dentry), &now, S_MTIME | S_CTIME);
+       path_put(&path);
 }
 
 static int btrfs_rm_dev_item(struct btrfs_device *device)
@@ -2077,7 +2082,7 @@ void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
        btrfs_kobject_uevent(bdev, KOBJ_CHANGE);
 
        /* Update ctime/mtime for device path for libblkid */
-       update_dev_time(bdev);
+       update_dev_time(device_path);
 }
 
 int btrfs_rm_device(struct btrfs_fs_info *fs_info,
@@ -2775,7 +2780,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
        btrfs_forget_devices(device_path);
 
        /* Update ctime/mtime for blkid or udev */
-       update_dev_time(bdev);
+       update_dev_time(device_path);
 
        return ret;