linux-kernel - Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions

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Message-ID: <20160406225424.GK24661@htj.duckdns.org>
Date:	Wed, 6 Apr 2016 18:54:24 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Waiman Long <waiman.long@....com>
Cc:	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Christoph Lameter <cl@...ux.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Toshimitsu Kani <toshi.kani@....com>
Subject: Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper
 functions

Hello,

On Wed, Apr 06, 2016 at 05:51:45PM -0400, Waiman Long wrote:
> >>+	/*
> >>+	 * If a statistics count is in the middle of being updated, it
> >>+	 * is possible that the above clearing may not work. So we need
> >>+	 * to double check again to make sure that the counters are really
> >>+	 * cleared. Still there is a still a very small chance that the
> >>+	 * second clearing does not work.
> >>+	 */
> >>+	for_each_possible_cpu(cpu) {
> >>+		unsigned long *pstats =  per_cpu_ptr(pcs->stats, cpu);
> >>+		int stat;
> >>+
> >>+		for (stat = 0; stat<  pcs->nstats; stat++, pstats++)
> >>+			if (*pstats)
> >>+				*pstats = 0;
> >>+	}
> >I don't think this is acceptable.
> 
> I am not sure what you mean here by not acceptable. Please enlighten me on
> that.

Hmmm... I thought that was pretty clear.  Try-twice-and-we-are-probably-okay
is simply not acceptable.  Please make it watertight.

Thanks.

-- 
tejun