splice: fix deadlock in splicing to file

There's a possible deadlock in generic_file_splice_write(),
splice_from_pipe() and ocfs2_file_splice_write():

 - task A calls generic_file_splice_write()
 - this calls inode_double_lock(), which locks i_mutex on both
   pipe->inode and target inode
 - ordering depends on inode pointers, can happen that pipe->inode is
   locked first
 - __splice_from_pipe() needs more data, calls pipe_wait()
 - this releases lock on pipe->inode, goes to interruptible sleep
 - task B calls generic_file_splice_write(), similarly to the first
 - this locks pipe->inode, then tries to lock inode, but that is
   already held by task A
 - task A is interrupted, it tries to lock pipe->inode, but fails, as
   it is already held by task B
 - ABBA deadlock

Fix this by explicitly ordering locks: the outer lock must be on
target inode and the inner lock (which is later unlocked and relocked)
must be on pipe->inode.  This is OK, pipe inodes and target inodes
form two nonoverlapping sets, generic_file_splice_write() and friends
are not called with a target which is a pipe.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Mark Fasheh <mfasheh@suse.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index a5887df2cd8a..8672b9536039 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -1926,7 +1926,7 @@ static ssize_t ocfs2_file_splice_write(struct pipe_inode_info *pipe,
                    out->f_path.dentry->d_name.len,
                    out->f_path.dentry->d_name.name);
 
-        inode_double_lock(inode, pipe->inode);
+        mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
 
         ret = ocfs2_rw_lock(inode, 1);
         if (ret < 0) {
@@ -1941,12 +1941,16 @@ static ssize_t ocfs2_file_splice_write(struct pipe_inode_info *pipe,
                 goto out_unlock;
         }
 
+        if (pipe->inode)
+                mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_CHILD);
         ret = generic_file_splice_write_nolock(pipe, out, ppos, len, flags);
+        if (pipe->inode)
+                mutex_unlock(&pipe->inode->i_mutex);
 
 out_unlock:
         ocfs2_rw_unlock(inode, 1);
 out:
-        inode_double_unlock(inode, pipe->inode);
+        mutex_unlock(&inode->i_mutex);
 
         mlog_exit(ret);
         return ret;