Re: [PATCH 1/2] ipc,shm: move BUG_ON check into shm_lock

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 29 May 2015 17:03:05 -0700 Davidlohr Bueso <dave@stgolabs.net> wrote:

> Upon every shm_lock call, we BUG_ON if an error was returned,
> indicating racing either in idr or in RMID. Move this logic
> into the locking.
> 
> ...
>
> --- 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 RMID,
> +		 * either way, the ID is busted.
> +		 */
> +		BUG_ON(1);
>  		return (struct shmid_kernel *)ipcp;
> +	}
>  

That's a bit odd.  Why not

--- a/ipc/shm.c~ipcshm-move-bug_on-check-into-shm_lock-fix-2
+++ a/ipc/shm.c
@@ -160,7 +160,7 @@ static inline struct shmid_kernel *shm_l
 		 * We raced in the idr lookup or with RMID,
 		 * either way, the ID is busted.
 		 */
-		BUG_ON(1);
+		BUG();
 		return (struct shmid_kernel *)ipcp;
 	}
 

and/or

--- a/ipc/shm.c~ipcshm-move-bug_on-check-into-shm_lock-fix
+++ a/ipc/shm.c
@@ -155,14 +155,11 @@ static inline struct shmid_kernel *shm_l
 {
 	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
 
-	if (IS_ERR(ipcp)) {
-		/*
-		 * We raced in the idr lookup or with RMID,
-		 * either way, the ID is busted.
-		 */
-		BUG();
-		return (struct shmid_kernel *)ipcp;
-	}
+	/*
+	 * We raced in the idr lookup or with RMID.  Either way, the ID is
+	 * busted.
+	 */
+	BUG_ON(IS_ERR(ipcp));
 
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
_