linux-kernel - Re: [PATCH v2] x86/platform/uv: Dont use smp_processor

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Date:   Thu, 22 Sep 2022 23:59:13 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Mike Travis <mike.travis@....com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steve Wahl <steve.wahl@....com>, x86@...nel.org,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        stable@...r.kernel.org, Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v2] x86/platform/uv: Dont use smp_processor_id while preemptible

On Thu, Sep 22, 2022 at 11:01 PM Mike Travis <mike.travis@....com> wrote:
>
> To avoid a "BUG: using smp_processor_id() in preemptible" debug warning
> message, disable preemption around use of the processor id.  This code
> sequence merely decides which portal that this CPU uses to read the RTC.
> It does this to avoid thrashing the cache but even if preempted it still
> reads the same time from the single RTC clock.

...

> Signed-off-by: Mike Travis <mike.travis@....com>
> Reviewed-by: Steve Wahl <steve.wahl@....com>
> Reviewed-by: Dimitri Sivanich <dimitri.sivanich@....com>
> Cc: stable@...r.kernel.org

No kernel version? No Fixes tag?

...

> -               offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;
> +               offset = (uv_cpu_blade_processor_id(cpu) * L1_CACHE_BYTES) % PAGE_SIZE;

Perhaps it can be transformed to use offset_in_page() at the same time.

-- 
With Best Regards,
Andy Shevchenko