linux-kernel - Re: [PATCH v2 03/14] notifiers: Assert that RCU is watching in notify

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Date:	Mon, 22 Jun 2015 13:36:50 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v2 03/14] notifiers: Assert that RCU is watching in
 notify_die

On Thu, Jun 18, 2015 at 12:08:35PM -0700, Andy Lutomirski wrote:
> Low-level arch entries often call notify_die, and it's easy for arch
> code to fail to exit an RCU quiescent state first.  Assert that
> we're not quiescent in notify_die.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  kernel/notifier.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/notifier.c b/kernel/notifier.c
> index ae9fc7cc360e..980e4330fb59 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -544,6 +544,8 @@ int notrace notify_die(enum die_val val, const char *str,
>  		.signr	= sig,
>  
>  	};
> +	rcu_lockdep_assert(rcu_is_watching(),
> +			   "notify_die called but RCU thinks we're quiescent");
>  	return atomic_notifier_call_chain(&die_chain, val, &args);
>  }

Ok, we're about to die and we will prepend what would be a more
important splat possibly hinting at the problem is with a lockdep splat.

I think we should do the assertion and make the rcu_lockdep splat come
last I but don't see how to do this easily from all the notify_die()
call sites.

Or am I missing something...?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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