Message-ID: <1379837823.5499.34.camel@marge.simpson.net>
Subject: Re: [PATCH] ipc/sem.c: fix update sem_otime when calling sem_op in
 semaphore initialization
From: Mike Galbraith <bitbucket@online.de>
To: Jia He <jiakernel@gmail.com>
Cc: linux-kernel@vger.kernel.org, Davidlohr Bueso <davidlohr.bueso@hp.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>,
        Manfred Spraul <manfred@colorfullife.com>,
        Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 22 Sep 2013 10:17:03 +0200
In-Reply-To: <1379815884-11035-1-git-send-email-jiakernel@gmail.com>
References: <1379815884-11035-1-git-send-email-jiakernel@gmail.com>
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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..

ipc,sem: Create semaphores with plausible sem_otime.

Signed-off-by: Mike Galbraith <bitbucket@online.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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