linux-kernel - Re: audit: rcu_read_lock() used illegally while idle

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Message-ID: <CALCETrVtKcwWsN4q7kp-K7kEfQyebKfSbBQy4iAhfP0WPVZNpQ@mail.gmail.com>
Date:	Wed, 3 Dec 2014 12:38:36 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Jones <davej@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Richard Guy Briggs <rgb@...hat.com>,
	Eric Paris <eparis@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: audit: rcu_read_lock() used illegally while idle

On Wed, Dec 3, 2014 at 12:19 PM, Dave Jones <davej@...hat.com> wrote:
> On Wed, Dec 03, 2014 at 12:06:56PM -0800, Andy Lutomirski wrote:
>
>  > >> Did something in RCU change recently ?
>  > >
>  > > Not since -rc1, as far as I know, anyway.
>  >
>  > I have patches to delete this whole fscking sysret fast but not really
>  > fast path.  I'll resend them for 3.19.  In the mean time, can you test
>  > this patch by itself:
>  >
>  > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/entry&id=1072a16a8d4ad1b11b8062f76e3236b9771b0fb6
>
> With that applied, I no longer see the trace.
>

Thanks.

The bug is that SCHEDULE_USER in sysret_schedule is wrong.  I'd
suggest adding a warning to schedule_user that fires if context
tracking thinks we're already in the kernel.

FWIW, I think that the rest of the SCHEDULE_USER calls may be wrong,
too.  In particular, the one in int_careful looks wrong as well, so I
don't see why my patch made a difference if I'm right.

Frédéric, any ideas here?  As a stopgap measure, making SCHEDULE_USER
restore the previous state might make sense for 3.18.

--Andy

> thanks,
>
>         Dave
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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