[patch 26/28] splice: remove i_mutex locking in splice_from_pipe()

Greg KH
2009-05-14T23:10:55Z

[-- Attachment #1: splice-remove-i_mutex-locking-in-splice_from_pipe.patch --]
[-- Type: text/plain, Size: 2064 bytes --]

2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Miklos Szeredi <miklos@szeredi.hu>

commit 2933970b960223076d6affcf7a77e2bc546b8102 upstream.

splice_from_pipe() is only called from two places:

- generic_splice_sendpage()
- splice_write_null()

Neither of these require i_mutex to be taken on the destination inode.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/splice.c | 18 ++----------------
1 file changed, 2 insertions(+), 16 deletions(-)

--- a/fs/splice.c
+++ b/fs/splice.c
@@ -782,7 +782,7 @@ EXPORT_SYMBOL(__splice_from_pipe);
* @actor: handler that splices the data
*
* Description:
- * See __splice_from_pipe. This function locks the input and output inodes,
+ * See __splice_from_pipe. This function locks the pipe inode,
* otherwise it's identical to __splice_from_pipe().
*
*/
@@ -791,7 +791,6 @@ ssize_t splice_from_pipe(struct pipe_ino
splice_actor *actor)
{
ssize_t ret;
- struct inode *inode = out->f_mapping->host;
struct splice_desc sd = {
.total_len = len,
.flags = flags,
@@ -799,24 +798,11 @@ ssize_t splice_from_pipe(struct pipe_ino
.u.file = out,
};

- /*
- * The actor worker might be calling ->prepare_write and
- * ->commit_write. Most of the time, these expect i_mutex to
- * be held. Since this may result in an ABBA deadlock with
- * pipe->inode, we have to order lock acquiry here.
- *
- * Outer lock must be inode->i_mutex, as pipe_wait() will
- * release and reacquire pipe->inode->i_mutex, AND inode must
- * never be a pipe.
- */
- WARN_ON(S_ISFIFO(inode->i_mode));
- mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
if (pipe->inode)
- mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_CHILD);
+ mutex_lock(&pipe->inode->i_mutex);
ret = __splice_from_pipe(pipe, &sd, actor);
if (pipe->inode)
mutex_unlock(&pipe->inode->i_mutex);
- mutex_unlock(&inode->i_mutex);

return ret;
}