Re: [BUG] signal: sighand unprotected when accessed by /proc

Steven Rostedt
2014-06-03T20:25:18Z

On Tue, 3 Jun 2014 22:09:38 +0200
Oleg Nesterov <oleg@redhat.com> wrote:

> > Now, if that lock is released and reused (I didn't trace other tasks
> > allocating these locks), it reinitializes the lock->wait_list.
>
> How? From where? This should be done by sighand_ctor() only?

This looks definitely like an -rt only bug and it's an obvious one at
that :-p

Looking in mm/slub.c: slab_alloc_node() we have this:

if (unlikely(gfpflags & __GFP_ZERO) && object)
memset(object, 0, s->object_size);
#ifdef CONFIG_PREEMPT_RT_FULL
if (unlikely(s->ctor) && object)
s->ctor(object);
#endif

slab_post_alloc_hook(s, gfpflags, object);

return object;
}

We call the ctor on the object when it is allocated, not when the page
is created.

Doh! I guess we now know why we shouldn't do that.

-- Steve