IPC/semaphores: move the rwmutex handling inside semctl_down
semctl_down is called with the rwmutex (the one which protects the list of
ipcs) taken in write mode.
This patch moves this rwmutex taken in write-mode inside semctl_down.
This has the advantages of reducing a little bit the window during which this
rwmutex is taken, clarifying sys_semctl, and finally of having a coherent
behaviour with [shm|msg]ctl_down
Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/sem.c b/ipc/sem.c
index 1b5ae35..77162ed 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -875,6 +875,11 @@
}
}
+/*
+ * This function handles some semctl commands which require the rw_mutex
+ * to be held in write mode.
+ * NOTE: no locks must be held, the rw_mutex is taken inside this function.
+ */
static int semctl_down(struct ipc_namespace *ns, int semid, int semnum,
int cmd, int version, union semun arg)
{
@@ -887,9 +892,12 @@
if(copy_semid_from_user (&setbuf, arg.buf, version))
return -EFAULT;
}
+ down_write(&sem_ids(ns).rw_mutex);
sma = sem_lock_check_down(ns, semid);
- if (IS_ERR(sma))
- return PTR_ERR(sma);
+ if (IS_ERR(sma)) {
+ err = PTR_ERR(sma);
+ goto out_up;
+ }
ipcp = &sma->sem_perm;
@@ -915,26 +923,22 @@
switch(cmd){
case IPC_RMID:
freeary(ns, ipcp);
- err = 0;
- break;
+ goto out_up;
case IPC_SET:
ipcp->uid = setbuf.uid;
ipcp->gid = setbuf.gid;
ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
| (setbuf.mode & S_IRWXUGO);
sma->sem_ctime = get_seconds();
- sem_unlock(sma);
- err = 0;
break;
default:
- sem_unlock(sma);
err = -EINVAL;
- break;
}
- return err;
out_unlock:
sem_unlock(sma);
+out_up:
+ up_write(&sem_ids(ns).rw_mutex);
return err;
}
@@ -968,9 +972,7 @@
return err;
case IPC_RMID:
case IPC_SET:
- down_write(&sem_ids(ns).rw_mutex);
err = semctl_down(ns,semid,semnum,cmd,version,arg);
- up_write(&sem_ids(ns).rw_mutex);
return err;
default:
return -EINVAL;