ipc: move the rcu_read_lock() from sem_lock_and_putref() into callers
Linus Torvalds [Sat, 4 May 2013 17:13:40 +0000 (10:13 -0700)]
This is another ipc semaphore locking cleanup, trying to make the
locking more straightforward.  We move the rcu read locking into the
callers of sem_lock_and_putref(), which in general means that we now
mostly do the rcu_read_lock() and rcu_read_unlock() in the same
function.

Mostly.  We still have the ipc_addid/newary/freeary mess, and things
like ipcctl_pre_down_nolock().

Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/sem.c

index 5cf7b4c..8f5aa34 100644 (file)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -322,7 +322,6 @@ static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns
 
 static inline void sem_lock_and_putref(struct sem_array *sma)
 {
-       rcu_read_lock();
        sem_lock(sma, NULL, -1);
        ipc_rcu_putref(sma);
 }
@@ -1117,6 +1116,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                                return -ENOMEM;
                        }
 
+                       rcu_read_lock();
                        sem_lock_and_putref(sma);
                        if (sma->sem_perm.deleted) {
                                sem_unlock(sma, -1);
@@ -1166,6 +1166,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                                goto out_free;
                        }
                }
+               rcu_read_lock();
                sem_lock_and_putref(sma);
                if (sma->sem_perm.deleted) {
                        sem_unlock(sma, -1);
@@ -1451,7 +1452,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
        }
 
        /* step 3: Acquire the lock on semaphore array */
-       /* This also does the rcu_read_lock() */
+       rcu_read_lock();
        sem_lock_and_putref(sma);
        if (sma->sem_perm.deleted) {
                sem_unlock(sma, -1);