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[PATCH] tee: link_pipe() must be careful when dropping one of the pipe locks

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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>
This commit is contained in:
Jens Axboe 2006-04-19 15:56:40 +02:00
parent c4f895cbe1
commit 2a27250e6c
1 changed files with 14 additions and 4 deletions
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18
fs/splice.c
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@ -1012,7 +1012,9 @@ static int link_pipe(struct pipe_inode_info *ipipe,
size_t len, unsigned int flags) size_t len, unsigned int flags)
{ {
struct pipe_buffer *ibuf, *obuf; 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 * 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). * could deadlock (one doing tee from A -> B, the other from B -> A).
*/ */
if (ipipe->inode < opipe->inode) { if (ipipe->inode < opipe->inode) {
ipipe_first = 1;
mutex_lock(&ipipe->inode->i_mutex); mutex_lock(&ipipe->inode->i_mutex);
mutex_lock(&opipe->inode->i_mutex); mutex_lock(&opipe->inode->i_mutex);
} else { } else {
@ -1068,9 +1071,11 @@ static int link_pipe(struct pipe_inode_info *ipipe,
/* /*
* We have input available, but no output room. * 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) if (!ret)
ret = -EAGAIN; ret = -EAGAIN;
break; break;
@ -1104,7 +1109,12 @@ static int link_pipe(struct pipe_inode_info *ipipe,
if (ret) if (ret)
break; 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) if (!ret)
ret = -EAGAIN; ret = -EAGAIN;
break; break;