linux-kernel - Re: [PATCH 1/4] lockdep, timer: Fix del_timer

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Message-ID: <20110204032834.GA2791@zhy>
Date:	Fri, 4 Feb 2011 11:28:34 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Faisal Latif <faisal.latif@...el.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Alessandro Rubini <rubini@...vis.unipv.it>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>,
	"David S. Miller" <davem@...emloft.net>,
	"John W. Linville" <linville@...driver.com>,
	Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH 1/4] lockdep, timer: Fix del_timer_sync() annotation

On Thu, Feb 03, 2011 at 03:09:41PM +0100, Peter Zijlstra wrote:
> Calling local_bh_enable() will want to actually start processing
> softirqs, which isn't a good idea since this can get called with IRQs
> disabled.
> 
> Cure this by using _local_bh_enable() which doesn't start processing
> softirqs, and use raw_local_irq_save() to avoid any softirqs from
> happending without letting lockdep think IRQs are in fact disabled.
> 
> Reported-by: Nick Bowler <nbowler@...iptictech.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> LKML-Reference: <new-submission>
> ---
>  kernel/timer.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/kernel/timer.c
> ===================================================================
> --- linux-2.6.orig/kernel/timer.c
> +++ linux-2.6/kernel/timer.c
> @@ -969,10 +969,14 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
>  int del_timer_sync(struct timer_list *timer)
>  {
>  #ifdef CONFIG_LOCKDEP
> +	unsigned long flags;
> +
> +	raw_local_irq_save(flags);
>  	local_bh_disable();
>  	lock_map_acquire(&timer->lockdep_map);
>  	lock_map_release(&timer->lockdep_map);
> -	local_bh_enable();
> +	_local_bh_enable();
> +	raw_local_irq_restore(flags);

This is more cheap than what I have done ;)
I think it will cure the issue reported by Nick.
Thanks you anyway.

Reviewed-by: Yong Zhang <yong.zhang0@...il.com>
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