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Date: Sat, 14 Sep 2013 16:42:56 +0800
From: Li Zefan <lizefan@huawei.com>
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To: John Stultz <john.stultz@linaro.org>
CC: lkml <linux-kernel@vger.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/2] [RFC v2] seqcount: Add lockdep functionality to seqcount/seqlock
 structures
References: <1379117948-7385-1-git-send-email-john.stultz@linaro.org>
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On 2013/9/14 8:19, John Stultz wrote:
> Currently seqlocks and seqcounts don't support lockdep.
> 
> After running across a seqcount related deadlock in the timekeeping
> code, I used a less-refined and more focused varient of this patch
> to narrow down the cause of the issue.
> 
> This is a first-pass attempt to properly enable lockdep functionality
> on seqlocks and seqcounts.
> 
> Since seqcounts are used in the vdso gettimeofday code, I've provided
> lockdep accessors.
> 
> I've also handled one cases where there were nested seqlock writers
> and there may be more edge cases.
> 
> Comments and feedback would be appreciated!
> 

Could you describe how seqlocks/seqcounts can lead to deadlock in the
changelog?

> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Li Zefan <lizefan@huawei.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
> v2:
>  * Update to new simplified lockdep.h
>  * vdso accessor simplifications
>  * removed needless preempt_disable
>  * removed unneeded ifdefs