From 32b7009196d0642a413cec6b97e650d6ad3ea663 Mon Sep 17 00:00:00 2001
From: Alasdair Kergon <agk@redhat.com>
Date: Fri, 8 Jul 2011 15:34:47 +0000
Subject: [PATCH] Log cookie values when incrementing/decrementing to give
 clues about races.

---
 libdm/libdm-common.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/libdm/libdm-common.c b/libdm/libdm-common.c
index 6ea184409..0aacd1f5e 100644
--- a/libdm/libdm-common.c
+++ b/libdm/libdm-common.c
@@ -1240,6 +1240,7 @@ static int _get_cookie_sem(uint32_t cookie, int *semid)
 static int _udev_notify_sem_inc(uint32_t cookie, int semid)
 {
 	struct sembuf sb = {0, 1, 0};
+	int val;
 
 	if (semop(semid, &sb, 1) < 0) {
 		log_error("semid %d: semop failed for cookie 0x%" PRIx32 ": %s",
@@ -1247,8 +1248,15 @@ static int _udev_notify_sem_inc(uint32_t cookie, int semid)
 		return 0;
 	}
 
-	log_debug("Udev cookie 0x%" PRIx32 " (semid %d) incremented",
-		  cookie, semid);
+ 	if ((val = semctl(semid, 0, GETVAL)) < 0) {
+		log_error("semid %d: sem_ctl GETVAL failed for "
+			  "cookie 0x%" PRIx32 ": %s",
+			  semid, cookie, strerror(errno));
+		return 0;		
+	}
+
+	log_debug("Udev cookie 0x%" PRIx32 " (semid %d) incremented to %d",
+		  cookie, semid, val);
 
 	return 1;
 }
@@ -1256,6 +1264,14 @@ static int _udev_notify_sem_inc(uint32_t cookie, int semid)
 static int _udev_notify_sem_dec(uint32_t cookie, int semid)
 {
 	struct sembuf sb = {0, -1, IPC_NOWAIT};
+	int val;
+
+ 	if ((val = semctl(semid, 0, GETVAL)) < 0) {
+		log_error("semid %d: sem_ctl GETVAL failed for "
+			  "cookie 0x%" PRIx32 ": %s",
+			  semid, cookie, strerror(errno));
+		return 0;
+	}
 
 	if (semop(semid, &sb, 1) < 0) {
 		switch (errno) {
@@ -1274,8 +1290,8 @@ static int _udev_notify_sem_dec(uint32_t cookie, int semid)
 		return 0;
 	}
 
-	log_debug("Udev cookie 0x%" PRIx32 " (semid %d) decremented",
-		  cookie, semid);
+	log_debug("Udev cookie 0x%" PRIx32 " (semid %d) decremented to %d",
+		  cookie, semid, val - 1);
 
 	return 1;
 }
@@ -1299,6 +1315,7 @@ static int _udev_notify_sem_create(uint32_t *cookie, int *semid)
 {
 	int fd;
 	int gen_semid;
+	int val;
 	uint16_t base_cookie;
 	uint32_t gen_cookie;
 	union semun sem_arg;
@@ -1359,8 +1376,15 @@ static int _udev_notify_sem_create(uint32_t *cookie, int *semid)
 		goto bad;
 	}
 
-	log_debug("Udev cookie 0x%" PRIx32 " (semid %d) incremented",
-		  gen_cookie, gen_semid);
+ 	if ((val = semctl(gen_semid, 0, GETVAL)) < 0) {
+		log_error("semid %d: sem_ctl GETVAL failed for "
+			  "cookie 0x%" PRIx32 ": %s",
+			  gen_semid, gen_cookie, strerror(errno));
+		return 0;		
+	}
+
+	log_debug("Udev cookie 0x%" PRIx32 " (semid %d) incremented to %d",
+		  gen_cookie, gen_semid, val);
 
 	if (close(fd))
 		stack;