linux-kernel - Re: [PATCH] audit: wait_for_auditd() should use TASK

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Message-ID: <20130531171025.GA32387@redhat.com>
Date:	Fri, 31 May 2013 19:10:25 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Guy Streeter <streeter@...hat.com>,
	Eric Paris <eparis@...hat.com>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] audit: wait_for_auditd() should use
	TASK_UNINTERRUPTIBLE

On 05/29, Andrew Morton wrote:
>
> On Fri, 24 May 2013 19:39:25 +0200 Oleg Nesterov <oleg@...hat.com> wrote:
>
> > audit_log_start() does wait_for_auditd() in a loop until
> > audit_backlog_wait_time passes or audit_skb_queue has a room.
> >
> > If signal_pending() is true this becomes a busy-wait loop,
> > schedule() in TASK_INTERRUPTIBLE won't block.
>
> And that's game over for a uniprocessor non-preempt machine, yes?

If this task is rt, yes. Otherwise schedule() still does pick_next_task()
but this is obviously bad anyway. So I fully agree with "Cc: stable" you
added.

> > Reported-by: Guy Streeter <streeter@...hat.com>
>
> And what did Guy report?  "that looks screwy"?  "my machine locked up"?

He also investigated the problem and provided the detailed explanation ;)

Oleg.

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