From d059c10283c1b9c979f237d20f8944465a2e3f62 Mon Sep 17 00:00:00 2001
From: kib <kib@FreeBSD.org>
Date: Sun, 27 Sep 2015 01:06:45 +0000
Subject: MFC r288044: Ensure that when a blockable open of fifo returns
 success, a valid file descriptor opened for complimentary access exists as
 well.

---
 sys/fs/fifofs/fifo_vnops.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

(limited to 'sys/fs')

diff --git a/sys/fs/fifofs/fifo_vnops.c b/sys/fs/fifofs/fifo_vnops.c
index e544bba..716faa3 100644
--- a/sys/fs/fifofs/fifo_vnops.c
+++ b/sys/fs/fifofs/fifo_vnops.c
@@ -64,6 +64,8 @@ struct fifoinfo {
 	struct pipe *fi_pipe;
 	long	fi_readers;
 	long	fi_writers;
+	u_int	fi_rgen;
+	u_int	fi_wgen;
 };
 
 static vop_print_t	fifo_print;
@@ -137,6 +139,7 @@ fifo_open(ap)
 	struct thread *td;
 	struct fifoinfo *fip;
 	struct pipe *fpipe;
+	u_int gen;
 	int error, stops_deferred;
 
 	vp = ap->a_vp;
@@ -164,6 +167,7 @@ fifo_open(ap)
 	PIPE_LOCK(fpipe);
 	if (ap->a_mode & FREAD) {
 		fip->fi_readers++;
+		fip->fi_rgen++;
 		if (fip->fi_readers == 1) {
 			fpipe->pipe_state &= ~PIPE_EOF;
 			if (fip->fi_writers > 0)
@@ -179,6 +183,7 @@ fifo_open(ap)
 			return (ENXIO);
 		}
 		fip->fi_writers++;
+		fip->fi_wgen++;
 		if (fip->fi_writers == 1) {
 			fpipe->pipe_state &= ~PIPE_EOF;
 			if (fip->fi_readers > 0)
@@ -187,6 +192,7 @@ fifo_open(ap)
 	}
 	if ((ap->a_mode & O_NONBLOCK) == 0) {
 		if ((ap->a_mode & FREAD) && fip->fi_writers == 0) {
+			gen = fip->fi_wgen;
 			VOP_UNLOCK(vp, 0);
 			stops_deferred = sigallowstop();
 			error = msleep(&fip->fi_readers, PIPE_MTX(fpipe),
@@ -194,7 +200,7 @@ fifo_open(ap)
 			if (stops_deferred)
 				sigdeferstop();
 			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
-			if (error) {
+			if (error != 0 && gen == fip->fi_wgen) {
 				fip->fi_readers--;
 				if (fip->fi_readers == 0) {
 					PIPE_LOCK(fpipe);
@@ -214,6 +220,7 @@ fifo_open(ap)
 			 */
 		}
 		if ((ap->a_mode & FWRITE) && fip->fi_readers == 0) {
+			gen = fip->fi_rgen;
 			VOP_UNLOCK(vp, 0);
 			stops_deferred = sigallowstop();
 			error = msleep(&fip->fi_writers, PIPE_MTX(fpipe),
@@ -221,7 +228,7 @@ fifo_open(ap)
 			if (stops_deferred)
 				sigdeferstop();
 			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
-			if (error) {
+			if (error != 0 && gen == fip->fi_rgen) {
 				fip->fi_writers--;
 				if (fip->fi_writers == 0) {
 					PIPE_LOCK(fpipe);
-- 
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