linux-kernel - Re: [PATCH 1/2] [RFC v2] seqcount: Add lockdep functionality to seqcount/seqlock structures

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Date:	Sat, 14 Sep 2013 16:42:56 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	John Stultz <john.stultz@...aro.org>
CC:	lkml <linux-kernel@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] [RFC v2] seqcount: Add lockdep functionality to seqcount/seqlock
 structures

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@...icios.com>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
> v2:
>  * Update to new simplified lockdep.h
>  * vdso accessor simplifications
>  * removed needless preempt_disable
>  * removed unneeded ifdefs

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