linux-kernel - Re: [PATCH] ipc/sem.c: fix update sem_otime when calling sem

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Date:	Sun, 22 Sep 2013 10:26:04 +0200
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Jia He <jiakernel@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] ipc/sem.c: fix update sem_otime when calling sem_op in
 semaphore initialization

On Sun, 2013-09-22 at 10:17 +0200, Mike Galbraith wrote: 
> On Sun, 2013-09-22 at 10:11 +0800, Jia He wrote: 
> > In commit 0a2b9d4c,the update of semaphore's sem_otime(last semop time)
> > was removed because he wanted to move setting sem->sem_otime to one
> > place. But after that, the initial semop() will not set the otime
> > because its sem_op value is 0(in semtimedop,will not change
> > otime if alter == 1).
> > 
> > the error case:
> > process_a(server)       process_b(client)
> > semget()
> > semctl(SETVAL)
> > semop()
> >                         semget()
> >                         setctl(IP_STAT)
> >                         for(;;) {               <--not successful here
> >                           check until sem_otime > 0
> >                         }
> 
> Why not..

(pokes evolution's don't-munge-me button)

ipc,sem: Create semaphores with plausible sem_otime.

Signed-off-by: Mike Galbraith <bitbucket@...ine.de>

diff --git a/ipc/sem.c b/ipc/sem.c
index 4108889..f2564d7 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -471,19 +471,20 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	ns->used_sems += nsems;
 
 	sma->sem_base = (struct sem *) &sma[1];
+	sma->complex_count = 0;
+	INIT_LIST_HEAD(&sma->pending_alter);
+	INIT_LIST_HEAD(&sma->pending_const);
+	INIT_LIST_HEAD(&sma->list_id);
+	sma->sem_nsems = nsems;
+	sma->sem_ctime = get_seconds();
 
 	for (i = 0; i < nsems; i++) {
 		INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
 		INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
 		spin_lock_init(&sma->sem_base[i].lock);
+		sma->sem_base[i].sem_otime = sma->sem_ctime;
 	}
 
-	sma->complex_count = 0;
-	INIT_LIST_HEAD(&sma->pending_alter);
-	INIT_LIST_HEAD(&sma->pending_const);
-	INIT_LIST_HEAD(&sma->list_id);
-	sma->sem_nsems = nsems;
-	sma->sem_ctime = get_seconds();
 	sem_unlock(sma, -1);
 	rcu_read_unlock();
 


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