IPC/semaphores: move the rwmutex handling inside semctl_down
Pierre Peiffer [Tue, 29 Apr 2008 08:00:49 +0000 (01:00 -0700)]
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>

ipc/sem.c

index 1b5ae35..77162ed 100644 (file)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -875,6 +875,11 @@ static inline unsigned long copy_semid_from_user(struct sem_setbuf *out, void __
        }
 }
 
+/*
+ * 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 @@ static int semctl_down(struct ipc_namespace *ns, int semid, int semnum,
                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 @@ static int semctl_down(struct ipc_namespace *ns, int semid, int semnum,
        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 @@ asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg)
                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;