X-Git-Url: http://pileus.org/git/?a=blobdiff_plain;ds=sidebyside;f=ipc%2Futil.c;h=4704223bfad48e41258e018266feb9f5ed4b860e;hb=ddf62f2c7bd041d35095b525ab33e3a3e0829aaa;hp=809ec5ec812295f7ef652b365ff0b35c4a6060d1;hpb=31881d74b6dd1a6c530cff61248def4f2da38bee;p=~andy%2Flinux

diff --git a/ipc/util.c b/ipc/util.c
index 809ec5ec812..4704223bfad 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -246,9 +246,8 @@ int ipc_get_maxid(struct ipc_ids *ids)
  *	is returned. The 'new' entry is returned in a locked state on success.
  *	On failure the entry is not locked and a negative err-code is returned.
  *
- *	Called with ipc_ids.rw_mutex held as a writer.
+ *	Called with writer ipc_ids.rw_mutex held.
  */
- 
 int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 {
 	kuid_t euid;
@@ -469,9 +468,7 @@ void ipc_free(void* ptr, int size)
 struct ipc_rcu {
 	struct rcu_head rcu;
 	atomic_t refcount;
-	/* "void *" makes sure alignment of following data is sane. */
-	void *data[0];
-};
+} ____cacheline_aligned_in_smp;
 
 /**
  *	ipc_rcu_alloc	-	allocate ipc and rcu space 
@@ -489,12 +486,14 @@ void *ipc_rcu_alloc(int size)
 	if (unlikely(!out))
 		return NULL;
 	atomic_set(&out->refcount, 1);
-	return out->data;
+	return out + 1;
 }
 
 int ipc_rcu_getref(void *ptr)
 {
-	return atomic_inc_not_zero(&container_of(ptr, struct ipc_rcu, data)->refcount);
+	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
+
+	return atomic_inc_not_zero(&p->refcount);
 }
 
 /**
@@ -508,7 +507,7 @@ static void ipc_schedule_free(struct rcu_head *head)
 
 void ipc_rcu_putref(void *ptr)
 {
-	struct ipc_rcu *p = container_of(ptr, struct ipc_rcu, data);
+	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
 
 	if (!atomic_dec_and_test(&p->refcount))
 		return;
@@ -747,8 +746,10 @@ int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
  * It must be called without any lock held and
  *  - retrieves the ipc with the given id in the given table.
  *  - performs some audit and permission check, depending on the given cmd
- *  - returns the ipc with both ipc and rw_mutex locks held in case of success
+ *  - returns the ipc with the ipc lock held in case of success
  *    or an err-code without any lock held otherwise.
+ *
+ * Call holding the both the rw_mutex and the rcu read lock.
  */
 struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
 				      struct ipc_ids *ids, int id, int cmd,
@@ -773,13 +774,10 @@ struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
 	int err = -EPERM;
 	struct kern_ipc_perm *ipcp;
 
-	down_write(&ids->rw_mutex);
-	rcu_read_lock();
-
 	ipcp = ipc_obtain_object_check(ids, id);
 	if (IS_ERR(ipcp)) {
 		err = PTR_ERR(ipcp);
-		goto out_up;
+		goto err;
 	}
 
 	audit_ipc_obj(ipcp);
@@ -790,16 +788,8 @@ struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
 	euid = current_euid();
 	if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid)  ||
 	    ns_capable(ns->user_ns, CAP_SYS_ADMIN))
-		return ipcp;
-
-out_up:
-	/*
-	 * Unsuccessful lookup, unlock and return
-	 * the corresponding error.
-	 */
-	rcu_read_unlock();
-	up_write(&ids->rw_mutex);
-
+		return ipcp; /* successful lookup */
+err:
 	return ERR_PTR(err);
 }