Re: [PATCH] RLIMIT_MEMLOCK accounting of shmctl() SHM_LOCK is broken

[Andrew Morton <akpm@osdl.org>]

Arjan van de Ven <arjan@infradead.org> wrote:
>
> On Mon, 2004-11-29 at 21:38 +0000, Linux Kernel Mailing List wrote:
> > ChangeSet 1.2251, 2004/11/29 13:38:43-08:00, mtk-lkml@gmx.net
> >  
> > -	spin_lock(&shmlock_user_lock);
> > -	locked = size >> PAGE_SHIFT;
> > +	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> >  	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
> >  	lock_limit >>= PAGE_SHIFT;
> > +	spin_lock(&shmlock_user_lock);
> 
> after this change... isn't the use to the
> current->signal->rlim[RLIMIT_MEMLOCK] entirely unlocked and thus racey ?

It always was - we don't modify rlimits under shmlock_user_lock.

If some other thread goes and changes RLIMIT_MEMLOCK under your feet then
this test will use either the old value or the new one, which is to be
expected.

(I get the feeling that I'm missing your point here)