netdev - Re: [PATCH v3 0/7] include: add setbits32/clrbits32/clrsetbits32/setbits64/clrbits64/clrsetbits64

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Message-ID: <20181115093034.GB23965@Red>
Date:   Thu, 15 Nov 2018 10:30:34 +0100
From:   LABBE Corentin <clabbe@...libre.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Gilles.Muller@...6.fr, Julia.Lawall@...6.fr, agust@...x.de,
        airlied@...ux.ie, alexandre.torgue@...com, alistair@...ple.id.au,
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        galak@...nel.crashing.org, joabreu@...opsys.com,
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Subject: Re: [PATCH v3 0/7] include: add
 setbits32/clrbits32/clrsetbits32/setbits64/clrbits64/clrsetbits64

On Wed, Oct 24, 2018 at 09:57:00AM +0100, Russell King - ARM Linux wrote:
> On Wed, Oct 24, 2018 at 07:35:46AM +0000, Corentin Labbe wrote:
> > This patchset adds a new set of functions which are open-coded in lot of
> > place.
> > Basicly the pattern is always the same, "read, modify a bit, write"
> > some driver and the powerpc arch already have thoses pattern them as functions. (like ahci_sunxi.c or dwmac-meson8b)
> 
> The advantage of them being open-coded is that it's _obvious_ to the
> reviewer that there is a read-modify-write going on which, in a multi-
> threaded environment, may need some locking (so it should trigger a
> review of the locking around that code.)
> 
> With it hidden inside a helper which has no locking itself, it becomes
> much easier to pass over in review, which means that races are much
> more likely to go unspotted - and that is bad news.
> 

Hello

I understand your fear, but I think the benefit overhaul thoses.
Furthermore, drivers which I have converted does not need such locking.

If you want I can rename the header to linux/setbits-non-atomic.h for making obvious the lack of locking.

Regards