linux-kernel - RE: [PATCH v8 6/7] apei/ghes: Use unrcu

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Date:   Wed, 12 Oct 2022 12:04:57 +0000
From:   Justin He <Justin.He@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Len Brown <lenb@...nel.org>, James Morse <James.Morse@....com>,
        Tony Luck <tony.luck@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Robert Richter <rric@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Jan Luebbe <jlu@...gutronix.de>,
        Khuong Dinh <khuong@...amperecomputing.com>,
        Kani Toshi <toshi.kani@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Shuai Xue <xueshuai@...ux.alibaba.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        nd <nd@....com>, kernel test robot <lkp@...el.com>
Subject: RE: [PATCH v8 6/7] apei/ghes: Use unrcu_pointer for cmpxchg

Hi Borislav

> -----Original Message-----
> From: Borislav Petkov <bp@...en8.de>
> Sent: Tuesday, October 11, 2022 10:46 PM
> To: Justin He <Justin.He@....com>
> Cc: Len Brown <lenb@...nel.org>; James Morse <James.Morse@....com>;
> Tony Luck <tony.luck@...el.com>; Mauro Carvalho Chehab
> <mchehab@...nel.org>; Robert Richter <rric@...nel.org>; Robert Moore
> <robert.moore@...el.com>; Qiuxu Zhuo <qiuxu.zhuo@...el.com>; Yazen
> Ghannam <yazen.ghannam@....com>; Jan Luebbe <jlu@...gutronix.de>;
> Khuong Dinh <khuong@...amperecomputing.com>; Kani Toshi
> <toshi.kani@....com>; Ard Biesheuvel <ardb@...nel.org>;
> linux-acpi@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-edac@...r.kernel.org; devel@...ica.org; Rafael J . Wysocki
> <rafael@...nel.org>; Shuai Xue <xueshuai@...ux.alibaba.com>; Jarkko
> Sakkinen <jarkko@...nel.org>; linux-efi@...r.kernel.org; nd <nd@....com>;
> kernel test robot <lkp@...el.com>
> Subject: Re: [PATCH v8 6/7] apei/ghes: Use unrcu_pointer for cmpxchg
> 
> On Tue, Oct 11, 2022 at 02:32:48PM +0000, Justin He wrote:
> > My original purpose is to make it pass the sparse checking.
> 
> Then do this pls.
> 
> This is a combined diff - do a second patch which does only remove the
> smp_wmb(). The smp_wmb() there is not needed as the cmpxchg() already
> implies a smp_mb() so there's no need for that separate, explicit one.
> 
I have a concern about what if cmpxchg failed? Do we have to still guarantee the ordering since cmpxchg will not imply a smp_mb if it failed.

Besides, I didn't find the paired smp_mb or smp_rmb
for this smp_wmb. Do you have any ideas?

--
Cheers,
Justin (Jia He)