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

[Davidlohr Bueso]

On Mon, 2015-06-01 at 15:52 -0700, Andrew Morton wrote:
> On Fri, 29 May 2015 17:03:05 -0700 Davidlohr Bueso <dave@xxxxxxxxxxxx> 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;
>  	}

Sure, this is fine.

Thanks,
Davidlohr

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