From 40944a1b03d3737b4c298f144690d574d7689913 Mon Sep 17 00:00:00 2001
From: Vasiliy Kulikov <segoon@openwall.com>
Date: Fri, 29 Jul 2011 03:56:40 +0400
Subject: [PATCH] --- yaml --- r: 261738 b: refs/heads/master c:
 4c677e2eefdba9c5bfc4474e2e91b26ae8458a1d h: refs/heads/master v: v3

---
 [refs]          |  2 +-
 trunk/ipc/shm.c | 61 +++++++++++++++++++++++--------------------------
 2 files changed, 29 insertions(+), 34 deletions(-)

diff --git a/[refs] b/[refs]
index 3885181b4cdd..7af210725928 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5774ed014f02120db9a6945a1ecebeb97c2acccb
+refs/heads/master: 4c677e2eefdba9c5bfc4474e2e91b26ae8458a1d
diff --git a/trunk/ipc/shm.c b/trunk/ipc/shm.c
index fdaf8be65b75..9fb044f3b345 100644
--- a/trunk/ipc/shm.c
+++ b/trunk/ipc/shm.c
@@ -131,6 +131,12 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
 
+static inline void shm_lock_by_ptr(struct shmid_kernel *ipcp)
+{
+	rcu_read_lock();
+	spin_lock(&ipcp->shm_perm.lock);
+}
+
 static inline struct shmid_kernel *shm_lock_check(struct ipc_namespace *ns,
 						int id)
 {
@@ -231,18 +237,15 @@ static void shm_close(struct vm_area_struct *vma)
 	up_write(&shm_ids(ns).rw_mutex);
 }
 
+/* Called with ns->shm_ids(ns).rw_mutex locked */
 static int shm_try_destroy_current(int id, void *p, void *data)
 {
 	struct ipc_namespace *ns = data;
-	struct shmid_kernel *shp = shm_lock(ns, id);
+	struct kern_ipc_perm *ipcp = p;
+	struct shmid_kernel *shp = container_of(ipcp, struct shmid_kernel, shm_perm);
 
-	if (IS_ERR(shp))
-		return 0;
-
-	if (shp->shm_creator != current) {
-		shm_unlock(shp);
+	if (shp->shm_creator != current)
 		return 0;
-	}
 
 	/*
 	 * Mark it as orphaned to destroy the segment when
@@ -255,64 +258,56 @@ static int shm_try_destroy_current(int id, void *p, void *data)
 	 * Don't even try to destroy it.  If shm_rmid_forced=0 and IPC_RMID
 	 * is not set, it shouldn't be deleted here.
 	 */
-	if (!ns->shm_rmid_forced) {
-		shm_unlock(shp);
+	if (!ns->shm_rmid_forced)
 		return 0;
-	}
 
-	if (shm_may_destroy(ns, shp))
+	if (shm_may_destroy(ns, shp)) {
+		shm_lock_by_ptr(shp);
 		shm_destroy(ns, shp);
-	else
-		shm_unlock(shp);
+	}
 	return 0;
 }
 
+/* Called with ns->shm_ids(ns).rw_mutex locked */
 static int shm_try_destroy_orphaned(int id, void *p, void *data)
 {
 	struct ipc_namespace *ns = data;
-	struct shmid_kernel *shp = shm_lock(ns, id);
-
-	if (IS_ERR(shp))
-		return 0;
+	struct kern_ipc_perm *ipcp = p;
+	struct shmid_kernel *shp = container_of(ipcp, struct shmid_kernel, shm_perm);
 
 	/*
 	 * We want to destroy segments without users and with already
 	 * exit'ed originating process.
+	 *
+	 * As shp->* are changed under rw_mutex, it's safe to skip shp locking.
 	 */
-	if (shp->shm_creator != NULL) {
-		shm_unlock(shp);
+	if (shp->shm_creator != NULL)
 		return 0;
-	}
 
-	if (shm_may_destroy(ns, shp))
+	if (shm_may_destroy(ns, shp)) {
+		shm_lock_by_ptr(shp);
 		shm_destroy(ns, shp);
-	else
-		shm_unlock(shp);
+	}
 	return 0;
 }
 
 void shm_destroy_orphaned(struct ipc_namespace *ns)
 {
 	down_write(&shm_ids(ns).rw_mutex);
-	idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
+	if (&shm_ids(ns).in_use)
+		idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
 	up_write(&shm_ids(ns).rw_mutex);
 }
 
 
 void exit_shm(struct task_struct *task)
 {
-	struct nsproxy *nsp = task->nsproxy;
-	struct ipc_namespace *ns;
-
-	if (!nsp)
-		return;
-	ns = nsp->ipc_ns;
-	if (!ns)
-		return;
+	struct ipc_namespace *ns = task->nsproxy->ipc_ns;
 
 	/* Destroy all already created segments, but not mapped yet */
 	down_write(&shm_ids(ns).rw_mutex);
-	idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
+	if (&shm_ids(ns).in_use)
+		idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
 	up_write(&shm_ids(ns).rw_mutex);
 }