[PATCH 1/5] ipc,shm: move BUG_ON check into shm_lock

[Davidlohr Bueso <dave@stgolabs.net>]

Upon every shm_lock call, we BUG_ON if an error was returned,
indicating racing either in idr or in shm_destroy. Move this logic
into the locking.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 ipc/shm.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/ipc/shm.c b/ipc/shm.c
index 6d76707..6dbac3b 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -155,8 +155,14 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
 {
 	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
 
-	if (IS_ERR(ipcp))
+	if (IS_ERR(ipcp)) {
+		/*
+		 * We raced in the idr lookup or with shm_destroy(),
+		 * either way, the ID is busted.
+		 */
+		BUG();
 		return (struct shmid_kernel *)ipcp;
+	}
 
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
@@ -191,7 +197,6 @@ static void shm_open(struct vm_area_struct *vma)
 	struct shmid_kernel *shp;
 
 	shp = shm_lock(sfd->ns, sfd->id);
-	BUG_ON(IS_ERR(shp));
 	shp->shm_atim = get_seconds();
 	shp->shm_lprid = task_tgid_vnr(current);
 	shp->shm_nattch++;
@@ -258,7 +263,6 @@ static void shm_close(struct vm_area_struct *vma)
 	down_write(&shm_ids(ns).rwsem);
 	/* remove from the list of attaches of the shm segment */
 	shp = shm_lock(ns, sfd->id);
-	BUG_ON(IS_ERR(shp));
 	shp->shm_lprid = task_tgid_vnr(current);
 	shp->shm_dtim = get_seconds();
 	shp->shm_nattch--;
@@ -1191,7 +1195,6 @@ out_fput:
 out_nattch:
 	down_write(&shm_ids(ns).rwsem);
 	shp = shm_lock(ns, shmid);
-	BUG_ON(IS_ERR(shp));
 	shp->shm_nattch--;
 	if (shm_may_destroy(ns, shp))
 		shm_destroy(ns, shp);
-- 
2.1.4

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