ipc: call idr_find() without locking in ipc_lock()
Nadia Derbey [Fri, 25 Jul 2008 08:48:03 +0000 (01:48 -0700)]
Call idr_find() locklessly from ipc_lock(), since the idr tree is now RCU
protected.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Acked-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Jim Houston <jim.houston@comcast.net>
Cc: Pierre Peiffer <peifferp@gmail.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/util.c

index 3339177..0f468c3 100644 (file)
@@ -688,10 +688,6 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
  * Look for an id in the ipc ids idr and lock the associated ipc object.
  *
  * The ipc object is locked on exit.
- *
- * This is the routine that should be called when the rw_mutex is not already
- * held, i.e. idr tree not protected: it protects the idr tree in read mode
- * during the idr_find().
  */
 
 struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
@@ -699,18 +695,13 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
        struct kern_ipc_perm *out;
        int lid = ipcid_to_idx(id);
 
-       down_read(&ids->rw_mutex);
-
        rcu_read_lock();
        out = idr_find(&ids->ipcs_idr, lid);
        if (out == NULL) {
                rcu_read_unlock();
-               up_read(&ids->rw_mutex);
                return ERR_PTR(-EINVAL);
        }
 
-       up_read(&ids->rw_mutex);
-
        spin_lock(&out->lock);
        
        /* ipc_rmid() may have already freed the ID while ipc_lock