ipc: move locking out of ipcctl_pre_down_nolock

This function currently acquires both the rw_mutex and the rcu lock on
successful lookups, leaving the callers to explicitly unlock them,
creating another two level locking situation.

Make the callers (including those that still use ipcctl_pre_down())
explicitly lock and unlock the rwsem and rcu lock.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 11 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 92ec6c69bab5..b4b892b5c5f8 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1289,39 +1289,44 @@ static int semctl_down(struct ipc_namespace *ns, int semid,
                         return -EFAULT;
         }
 
+        down_write(&sem_ids(ns).rw_mutex);
+        rcu_read_lock();
+
         ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
                                       &semid64.sem_perm, 0);
-        if (IS_ERR(ipcp))
-                return PTR_ERR(ipcp);
+        if (IS_ERR(ipcp)) {
+                err = PTR_ERR(ipcp);
+                /* the ipc lock is not held upon failure */
+                goto out_unlock1;
+        }
 
         sma = container_of(ipcp, struct sem_array, sem_perm);
 
         err = security_sem_semctl(sma, cmd);
-        if (err) {
-                rcu_read_unlock();
-                goto out_up;
-        }
+        if (err)
+                goto out_unlock1;
 
-        switch(cmd){
+        switch (cmd) {
         case IPC_RMID:
                 sem_lock(sma, NULL, -1);
+                /* freeary unlocks the ipc object and rcu */
                 freeary(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 sem_lock(sma, NULL, -1);
                 err = ipc_update_perm(&semid64.sem_perm, ipcp);
                 if (err)
-                        goto out_unlock;
+                        goto out_unlock0;
                 sma->sem_ctime = get_seconds();
                 break;
         default:
-                rcu_read_unlock();
                 err = -EINVAL;
-                goto out_up;
+                goto out_unlock1;
         }
 
-out_unlock:
+out_unlock0:
         sem_unlock(sma, -1);
+out_unlock1:
         rcu_read_unlock();
 out_up:
         up_write(&sem_ids(ns).rw_mutex);