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authorJens Axboe <axboe@suse.de>2006-04-19 15:56:40 +0200
committerJens Axboe <axboe@suse.de>2006-04-19 15:56:40 +0200
commit2a27250e6cf47ca1ea3bea0a55e4b7889c097627 (patch)
tree3dbd4747df21e72420ab6fb91fc174173903c803 /fs/splice.c
parentc4f895cbe1e95aab633207fb19c650b7c984c01a (diff)
[PATCH] tee: link_pipe() must be careful when dropping one of the pipe locks
We need to ensure that we only drop a lock that is ordered last, to avoid ABBA deadlocks with competing processes. Signed-off-by: Jens Axboe <axboe@suse.de>
Diffstat (limited to 'fs/splice.c')
-rw-r--r--fs/splice.c18
1 files changed, 14 insertions, 4 deletions
diff --git a/fs/splice.c b/fs/splice.c
index 78cd264340f..4f5e6b09fb2 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1012,7 +1012,9 @@ static int link_pipe(struct pipe_inode_info *ipipe,
size_t len, unsigned int flags)
{
struct pipe_buffer *ibuf, *obuf;
- int ret = 0, do_wakeup = 0, i;
+ int ret, do_wakeup, i, ipipe_first;
+
+ ret = do_wakeup = ipipe_first = 0;
/*
* Potential ABBA deadlock, work around it by ordering lock
@@ -1020,6 +1022,7 @@ static int link_pipe(struct pipe_inode_info *ipipe,
* could deadlock (one doing tee from A -> B, the other from B -> A).
*/
if (ipipe->inode < opipe->inode) {
+ ipipe_first = 1;
mutex_lock(&ipipe->inode->i_mutex);
mutex_lock(&opipe->inode->i_mutex);
} else {
@@ -1068,9 +1071,11 @@ static int link_pipe(struct pipe_inode_info *ipipe,
/*
* We have input available, but no output room.
- * If we already copied data, return that.
+ * If we already copied data, return that. If we
+ * need to drop the opipe lock, it must be ordered
+ * last to avoid deadlocks.
*/
- if (flags & SPLICE_F_NONBLOCK) {
+ if ((flags & SPLICE_F_NONBLOCK) || !ipipe_first) {
if (!ret)
ret = -EAGAIN;
break;
@@ -1104,7 +1109,12 @@ static int link_pipe(struct pipe_inode_info *ipipe,
if (ret)
break;
}
- if (flags & SPLICE_F_NONBLOCK) {
+ /*
+ * pipe_wait() drops the ipipe mutex. To avoid deadlocks
+ * with another process, we can only safely do that if
+ * the ipipe lock is ordered last.
+ */
+ if ((flags & SPLICE_F_NONBLOCK) || ipipe_first) {
if (!ret)
ret = -EAGAIN;
break;