From: Eric Wong <normalperson@yhbt.net>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Dave Jones <davej@redhat.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Davide Libenzi <davidel@xmailserver.org>,
Pekka Enberg <penberg@cs.helsinki.fi>,
Peter Hurley <peter@hurleysoftware.com>,
Eric Dumazet <edumazet@google.com>
Subject: Re: epoll oops.
Date: Wed, 16 Oct 2013 22:39:22 +0000 [thread overview]
Message-ID: <20131016223922.GA18383@dcvr.yhbt.net> (raw)
In-Reply-To: <20131015154838.GA32271@redhat.com>
Oleg Nesterov <oleg@redhat.com> wrote:
> Yes. Before that 971316f0503a hack epoll can't even know if the task
> which did signalfd_poll() exits and frees the active signalfd_wqh.
> If for example that task forked a child before exit.
>
> And the whole RCU logic is only needed if exit/ep_remove_wait_queue
> actually race with each other.
Is there any chance this oops is caused by (or at least more easily
exposed by) commit 91cf5ab60ff82ecf4550a596867787c1e360dd3f ?
(epoll: add a reschedule point in ep_free())
I thought 91cf5ab would be benign, except...
> Yes, ugly, agreed. d80e731ecab4 even tries to docunent that this all
> is the hack.
.. the following sentence from d80e731ecab4 caught my eye:
It also assumes that nobody can take tasklist_lock under epoll
locks, this seems to be true.
I haven't been able to trace if cond_resched() can take tasklist_lock.
next prev parent reply other threads:[~2013-10-16 22:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-14 15:46 epoll oops Dave Jones
2013-10-14 17:31 ` Linus Torvalds
2013-10-14 19:17 ` Oleg Nesterov
2013-10-14 20:57 ` Linus Torvalds
2013-10-15 15:48 ` Oleg Nesterov
2013-10-15 19:28 ` Dave Jones
2013-10-16 22:39 ` Eric Wong [this message]
2013-10-17 13:53 ` Oleg Nesterov
2013-10-23 9:08 ` Pekka Enberg
2013-10-23 13:43 ` Peter Hurley
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