lkml.org 
[lkml]   [2014]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: introduce task_rcu_dereference?
From
Date
В Чт, 23/10/2014 в 20:18 +0200, Oleg Nesterov пишет:
> On 10/23, Kirill Tkhai wrote:
> >
> > I'm agree generic helper is better. But probe_slab_address() has a sence
> > if we know that SDBR is worse in our subject area.
>
> And I still think it is worse.
>
> > Less of code is
> > easier to support :)
>
> Sure, but ignoring the comments, SDBR needs the same code in
> task_rcu_dereference() ? Except, of course
>
> - probe_slab_address(&task->sighand, sighand);
> + sighand = task->sighand;
>
> or how do you think we can simplify it?

Ok, really, not big simplification there. Your variant is good.

> > probe_slab_address() it's not a trivial logic.
>
> But it already has a user. And probably it can have more.
>
> To me the usage of SDBR is not trivial (and confusing) in this case.
> Once again, ignoring the CONFIG_DEBUG_PAGEALLOC problems it does not
> help at all.
>
> With or without SDBR rq->curr can be reused and we need to avoid this
> race. The fact that with SDBR it can be reused only as another instance
> of task_struct is absolutely immaterial imo.
>
> Not to mention that SDBR still adds some overhead while probe_slab()
> is free unless CONFIG_DEBUG_PAGEALLOC, but this option adds a large
> slowdown anyway.
>
>
> But again, I can't really work today, perhaps I missed something.
> Perhaps you can show a better code which relies on SDBR?

No, it would be the same except probe_slab_address(). So, let's stay
on probe_slab_address() variant and fix the bug this way.

Kirill

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2014-10-24 10:21    [W:0.041 / U:3.128 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site