linux-kernel - Re: [PATCH v2 00/33] locking/atomic: convert all architectures to ARCH

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Message-ID: <8a056e32-26bf-3038-984e-fcf8cac988d0@infradead.org>
Date:   Sun, 27 Jun 2021 14:47:11 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, will@...nel.org,
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Subject: Re: [PATCH v2 00/33] locking/atomic: convert all architectures to
 ARCH_ATOMIC

On 6/18/21 1:48 AM, Mark Rutland wrote:
> On Fri, Jun 04, 2021 at 10:56:16PM -0700, Randy Dunlap wrote:
>> On 5/25/21 7:01 AM, Mark Rutland wrote:
>>> This series (based on v5.13-rc2) converts all architectures to
>>> ARCH_ATOMIC. This will allow the use of instrumented atomics on all
>>> architectures (e.g. for KASAN and similar), and simplifies the core
>>> atomic code (which should allow for easier rework of the fallbacks and
>>> other bits in future).
> 
> [...]
> 
>> Hi Mark,
>> Sorry for the late reply. 
> 
> Hi Randy,
> 
> Likewise, apologies in the delay in getting to this!
> 
>> I was just trying to update a patch
>> to arch/sh/include/asm/cmpxchg.h, in its xchg() macro:
>>
>> https://lore.kernel.org/lkml/20210602231443.4670-2-rdunlap@infradead.org/
>>
>> The patch simply converts xchg() to a GCC statement expression to
>> eliminate a build warning.

Hm, with your locking/atomic patch series applied (in linux-next), I can
no longer make arch/sh/ get this build warning:

../fs/ocfs2/file.c: In function 'ocfs2_file_write_iter':
../arch/sh/include/asm/cmpxchg.h:49:3: warning: value computed is not used [-Wunused-value]
   49 |  ((__typeof__(*(ptr)))__xchg((ptr),(unsigned long)(x), sizeof(*(ptr))))


so I will go ahead with the rest of my arch/sh/ patches and then contemplate
what to do about this one.


>> Arnd has done this for m68k and I have done it for sparc in the past.
>>
>> Is there any (good) reason that all versions of arch_xchg() are not
>> statement expressions?  In this patch series, they seem to be quite
>> mixed (as they were before this patch series). I count 11 arches
>> that use a statement expression and 4 that do not (including arch/sh/).
> 
> Largely I tried to make the minimal change from what was there before,
> and I didn't have any specific reason to either use or avoid statement
> expressions.
> 
> This series has been queued in the tip tree's locking/core branch for a
> while now, but we could spin a patch atop. Do you want to spin a patch
> to convert the remaining 4 architectures in one go?

I'll look at the 4 remaining arches later..

thanks.
-- 
~Randy