From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Sun, 16 Aug 2009 03:56:04 +0000 (-0700)
Subject: PIPE - Fix a blocking race.
X-Git-Url: https://gitweb.dragonflybsd.org/~polachok/dragonfly.git/commitdiff_plain/958de3056ed7f8ed4e39ff27855adf89b5d6cd0e

PIPE - Fix a blocking race.

* A pipe can get stuck in "pipewr" due to a race caused by a selwakeup()
  before a tsleep().  Fix the race.
---

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index 97a219e402..bf24ac257f 100644
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -871,10 +871,11 @@ pipe_write(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
 		 * wake up select/poll.
 		 */
 		if (space == 0) {
-			pipeselwakeup(wpipe);
-			++wpipe->pipe_wantwcnt;
 			wpipe->pipe_state |= PIPE_WANTW;
-			error = tsleep(wpipe, PCATCH, "pipewr", 0);
+			++wpipe->pipe_wantwcnt;
+			pipeselwakeup(wpipe);
+			if (wpipe->pipe_state & PIPE_WANTW)
+				error = tsleep(wpipe, PCATCH, "pipewr", 0);
 			++pipe_wblocked_count;
 		}
 		lwkt_reltoken(&rlock);