linux-kernel - Re: [PATCH 4/4] epoll: ep_unregister_pollwait() can use the freed pwq->whead

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Date:	Thu, 23 Feb 2012 14:17:03 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Greg KH <greg@...ah.com>, Jason Baron <jbaron@...hat.com>,
	Roland McGrath <roland@...k.frob.com>,
	Eugene Teo <eugeneteo@...nel.sg>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] epoll: ep_unregister_pollwait() can use the freed pwq->whead

On Thu, Feb 23, 2012 at 7:44 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> Or we can rely on the fact that sighand_cachep is SLAB_DESTROY_BY_RCU,
> and assume that ->whead is always rcu-protected if it can go away.
>
> In this case we don't need 3/4 (although it makes sense to add the
> fat comment), and 4/4 can be simplified, see below.

Ok.

Can you also get rid of 1/4, because quite frankly, adding that
BUG_ON() is just annoying. Either the thing gets fixed or not, but at
no point is it ok to say "ok, I'm going to fix it, but before I do
I'll just make it much worse".

Hmm?
               Linus
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