[PATCH v2 6/4] ipc: open code and rename sem_lock

[Rik van Riel <riel@redhat.com>]

Rename sem_lock to sem_obtain_lock, so we can introduce a sem_lock
function later that only locks the sem_array and does nothing else.

Open code the locking from ipc_lock in sem_obtain_lock, so we can
introduce finer grained locking for the sem_array in the next patch.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 ipc/sem.c |   23 +++++++++++++++++++----
 1 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index efb49e7..d92ba32 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -194,14 +194,29 @@ void __init sem_init (void)
  * sem_lock_(check_) routines are called in the paths where the rw_mutex
  * is not held.
  */
-static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id)
+static inline struct sem_array *sem_obtain_lock(struct ipc_namespace *ns, int id)
 {
-	struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id);
+	struct kern_ipc_perm *ipcp;
 
+	rcu_read_lock();
+	ipcp = ipc_obtain_object(&sem_ids(ns), id);
 	if (IS_ERR(ipcp))
-		return (struct sem_array *)ipcp;
+		goto err1;
+
+	write_lock(&ipcp->lock);
+
+	/* ipc_rmid() may have already freed the ID while write_lock
+	 * was spinning: verify that the structure is still valid
+	 */
+	if (ipcp->deleted)
+		goto err0;
 
 	return container_of(ipcp, struct sem_array, sem_perm);
+err0:
+	write_unlock(&ipcp->lock);
+err1:
+	rcu_read_unlock();
+	return ERR_PTR(-EINVAL);
 }
 
 static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
@@ -1558,7 +1573,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 		goto out_free;
 	}
 
-	sma = sem_lock(ns, semid);
+	sma = sem_obtain_lock(ns, semid);
 
 	/*
 	 * Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.