linux-kernel - [ 49/50] ipc/sem.c: update sem

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Message-Id: <20131016174404.366753549@linuxfoundation.org>
Date:	Wed, 16 Oct 2013 10:45:35 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Manfred Spraul <manfred@...orfullife.com>,
	Jia He <jiakernel@...il.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 49/50] ipc/sem.c: update sem_otime for all operations

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Manfred Spraul <manfred@...orfullife.com>

commit 0e8c665699e953fa58dc1b0b0d09e5dce7343cc7 upstream.

In commit 0a2b9d4c7967 ("ipc/sem.c: move wake_up_process out of the
spinlock section"), the update of semaphore's sem_otime(last semop time)
was moved to one central position (do_smart_update).

But since do_smart_update() is only called for operations that modify
the array, this means that wait-for-zero semops do not update sem_otime
anymore.

The fix is simple:
Non-alter operations must update sem_otime.

[akpm@...ux-foundation.org: coding-style fixes]
Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Reported-by: Jia He <jiakernel@...il.com>
Tested-by: Jia He <jiakernel@...il.com>
Cc: Davidlohr Bueso <davidlohr.bueso@...com>
Cc: Mike Galbraith <efault@....de>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 ipc/sem.c |   42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -918,6 +918,24 @@ again:
 }
 
 /**
+ * set_semotime(sma, sops) - set sem_otime
+ * @sma: semaphore array
+ * @sops: operations that modified the array, may be NULL
+ *
+ * sem_otime is replicated to avoid cache line trashing.
+ * This function sets one instance to the current time.
+ */
+static void set_semotime(struct sem_array *sma, struct sembuf *sops)
+{
+	if (sops == NULL) {
+		sma->sem_base[0].sem_otime = get_seconds();
+	} else {
+		sma->sem_base[sops[0].sem_num].sem_otime =
+							get_seconds();
+	}
+}
+
+/**
  * do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue
  * @sma: semaphore array
  * @sops: operations that were performed
@@ -967,17 +985,10 @@ static void do_smart_update(struct sem_a
 			}
 		}
 	}
-	if (otime) {
-		if (sops == NULL) {
-			sma->sem_base[0].sem_otime = get_seconds();
-		} else {
-			sma->sem_base[sops[0].sem_num].sem_otime =
-								get_seconds();
-		}
-	}
+	if (otime)
+		set_semotime(sma, sops);
 }
 
-
 /* The following counts are associated to each semaphore:
  *   semncnt        number of tasks waiting on semval being nonzero
  *   semzcnt        number of tasks waiting on semval being zero
@@ -1839,12 +1850,17 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
 
 	error = perform_atomic_semop(sma, sops, nsops, un,
 					task_tgid_vnr(current));
-	if (error <= 0) {
-		if (alter && error == 0)
+	if (error == 0) {
+		/* If the operation was successful, then do
+		 * the required updates.
+		 */
+		if (alter)
 			do_smart_update(sma, sops, nsops, 1, &tasks);
-
-		goto out_unlock_free;
+		else
+			set_semotime(sma, sops);
 	}
+	if (error <= 0)
+		goto out_unlock_free;
 
 	/* We need to sleep on this operation, so we put the current
 	 * task into the pending queue and go to sleep.


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