ipc: move the rcu_read_lock() from sem_lock_and_putref() into callers

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>

1 files changed, 3 insertions, 2 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 5cf7b4c093b3..8f5aa34f8d30 100644
--- 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);