linux-kernel - Re: [PATCH] exit.c: call proc_exit_connector() after exit

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Message-ID: <20140315191222.GA32499@redhat.com>
Date:	Sat, 15 Mar 2014 20:12:22 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	matt.helsley@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Evgeniy Polyakov <zbr@...emap.net>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] exit.c: call proc_exit_connector() after exit_state is
	set

On 03/15, Linus Torvalds wrote:
>
> [ Going through old emails, adding relevant people, ie Oleg for
> kernel/exit.c and David because he seems to be the go-to person for
> connector issues judging by commits ]
>
> Patch looks sane to me, and logically that exit_connector thing would
> pair with exit_notify(), but I'd like some comments on it.

Please see the (confusing, my fault) discussion

	http://marc.info/?t=139327886600003

But in short, personally I agree with this change too. Just it was not
clear from the changelog (to me ;) which problem this change actually
tries to solve, because in general the task is not waitable after it
reports PROC_EVENT_EXIT.

So I think the patch is fine, but let me repeat:

	I hope that someone
	can confirm that netlink_broadcast() is safe even if release_task(current)
	was already called, so that the caller has no pids, sighand, is not visible
	via /proc/, etc.

not that I expect this should not work, but still.

> That
> usability issue/race has been there since forever afaik. We probably
> should never have added that process events connector thing, but since
> we did and people apparently use it..

Yes... BTW, Guillaume, I forgot to mention that perhaps you can use
signalfd(SIGCHLD) instead of connector, this is epoll-able too. SIGCHLD
doesn't queue, so it can't tell you which child has exited, but WNOHANG
should work.

Oleg.

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