From 2a27250e6cf47ca1ea3bea0a55e4b7889c097627 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 19 Apr 2006 15:56:40 +0200 Subject: [PATCH] [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 --- fs/splice.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/fs/splice.c b/fs/splice.c index 78cd264340..4f5e6b09fb 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; -- 2.39.5