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From: Jonas Malaco <jonas@protocubo.io>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Jean Delvare <jdelvare@suse.com>,
	linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hwmon: (nzxt-kraken2) mark and order concurrent accesses
Date: Tue, 30 Mar 2021 14:53:02 -0300	[thread overview]
Message-ID: <20210330175302.ihsmijnidxjhmcqa@calvin.localdomain> (raw)
In-Reply-To: <38c76eb1-808a-1c9a-2494-208270a66e14@roeck-us.net>

On Tue, Mar 30, 2021 at 03:51:21AM -0700, Guenter Roeck wrote:
> [ ... ]
> 
> Then please explain why _this_ use of time_after() is wrong but all
> others in the kernel are not. Also, please note that we are not
> concerned with code generation by the compiler as long as the
> generated code is correct (and I don't see any indication that
> it isn't).

The accesses to priv->temp_input[], ->fan_input[] and ->updated (where
this relates to your question about time_after()) are not wrong, but
undefined.

But if we are not concerned with code that is currently generated
correctly, which indeed is the case in the five arch x compiler
combinations I tested, then there simply is no point to this patch.

Thanks for going through this with me,
Jonas

P.S. Admittedly from a sample way too small, but in the kernel
time_after(jiffies, x) calls do not generally appear to involve an
expression x with a data race.  And there are a few calls where
READ_ONCE() is indeed used in x.

      reply	other threads:[~2021-03-30 17:53 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-29  8:22 [PATCH] hwmon: (nzxt-kraken2) mark and order concurrent accesses Jonas Malaco
2021-03-29 21:53 ` Guenter Roeck
2021-03-30  0:21   ` Jonas Malaco
2021-03-30  1:01     ` Guenter Roeck
2021-03-30  3:16       ` Jonas Malaco
2021-03-30  5:43         ` Guenter Roeck
2021-03-30  6:27           ` Jonas Malaco
2021-03-30 10:51             ` Guenter Roeck
2021-03-30 17:53               ` Jonas Malaco [this message]

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