Btrfs: fix deadlock between clone/dedupe and rename

BugLink: https://bugs.launchpad.net/bugs/1821607
commit 4ea748e1d2c9f8a27332b949e8210dbbf392987e upstream.

Reflinking (clone/dedupe) and rename are operations that operate on two
inodes and therefore need to lock them in the same order to avoid ABBA
deadlocks. It happens that Btrfs' reflink implementation always locked
them in a different order from VFS's lock_two_nondirectories() helper,
which is used by the rename code in VFS, resulting in ABBA type deadlocks.

Btrfs' locking order:

  static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
  {
         if (inode1 < inode2)
                swap(inode1, inode2);

         inode_lock_nested(inode1, I_MUTEX_PARENT);
         inode_lock_nested(inode2, I_MUTEX_CHILD);
  }

VFS's locking order:

  void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
  {
        if (inode1 > inode2)
                swap(inode1, inode2);

        if (inode1 && !S_ISDIR(inode1->i_mode))
                inode_lock(inode1);
        if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
                inode_lock_nested(inode2, I_MUTEX_NONDIR2);
}

Fix this by killing the btrfs helper function that does the double inode
locking and replace it with VFS's helper lock_two_nondirectories().

Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Fixes: 416161db9b63e3 ("btrfs: offline dedupe")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 9c8e1734429c7649721eeadd3dca941ff2ee490c..6e111949672113b660220495080334f00a9c4b4c 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3206,21 +3206,6 @@ out:
        return ret;
 }
 
-static void btrfs_double_inode_unlock(struct inode *inode1, struct inode *inode2)
-{
-       inode_unlock(inode1);
-       inode_unlock(inode2);
-}
-
-static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
-{
-       if (inode1 < inode2)
-               swap(inode1, inode2);
-
-       inode_lock_nested(inode1, I_MUTEX_PARENT);
-       inode_lock_nested(inode2, I_MUTEX_CHILD);
-}
-
 static void btrfs_double_extent_unlock(struct inode *inode1, u64 loff1,
                                       struct inode *inode2, u64 loff2, u64 len)
 {
@@ -3989,7 +3974,7 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
        if (same_inode)
                inode_lock(inode_in);
        else
-               btrfs_double_inode_lock(inode_in, inode_out);
+               lock_two_nondirectories(inode_in, inode_out);
 
        /*
         * Now that the inodes are locked, we need to start writeback ourselves
@@ -4039,7 +4024,7 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
        if (same_inode)
                inode_unlock(inode_in);
        else
-               btrfs_double_inode_unlock(inode_in, inode_out);
+               unlock_two_nondirectories(inode_in, inode_out);
 
        return ret;
 }
@@ -4069,7 +4054,7 @@ loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
        if (same_inode)
                inode_unlock(src_inode);
        else
-               btrfs_double_inode_unlock(src_inode, dst_inode);
+               unlock_two_nondirectories(src_inode, dst_inode);
 
        return ret < 0 ? ret : len;
 }