linux-kernel - Re: [PATCH 1/4] for 2.6.18, revert "Drop tasklist lock in do_sched

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Date:	Sat, 19 Aug 2006 23:43:13 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...l.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] for 2.6.18, revert "Drop tasklist lock in do_sched_setscheduler"

On 08/19, Oleg Nesterov wrote:
>
> sched_setscheduler() looks at ->signal->rlim[]. It is unsafe do dereference
> ->signal unless tasklist_lock or ->siglock is held (or p == current). We pin
> the task structure, but this can't prevent from release_task()->__exit_signal()
> which sets ->signal = NULL.

See the testcase below, 2.6.18-rc4 oopses. The stable tree is ok, the problem
was introduced during 2.6.18 development.

Oleg.

#!/usr/bin/perl

pipe R, W;

if (fork) {
	while (sysread R, $_, 4) {
		do {
			syscall 156, unpack('i', $_), 1, pack('i', 1);
		} while $! == 1; # EPERM
	}
} else {
	wait while fork;
	syswrite W, pack 'i', $$;
}

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