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

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Date:   Sat, 21 May 2022 15:57:55 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Mike Travis <mike.travis@....com>, 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
Cc:     Dimitri Sivanich <dimitri.sivanich@....com>,
        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] x86/platform/uv: Dont use smp_processor_id while
 preemptable

Hi Mike,

On 5/20/22 22:37, Mike Travis wrote:
> To avoid a "BUG: using smp_processor_id() in preemptible" debug
> warning message, disable preemption around use of the processor id.
> 
> Signed-off-by: Mike Travis <mike.travis@....com>
> Reviewed-by: Steve Wahl <steve.wahl@....com>
> Reviewed-by: Dimitri Sivanich <dimitri.sivanich@....com>

A git blame shows that this code has been around for quite
a while; so presumably this should be backported to some of
the stable kernel series ?

Maybe add an appropriate Cc: stable tag with the range of
kernels this should be added to and/or add a Fixes: tag?

Regards,

Hans


> ---
>  arch/x86/platform/uv/uv_time.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c
> index 54663f3e00cb..094190814a28 100644
> --- a/arch/x86/platform/uv/uv_time.c
> +++ b/arch/x86/platform/uv/uv_time.c
> @@ -275,14 +275,17 @@ static int uv_rtc_unset_timer(int cpu, int force)
>   */
>  static u64 uv_read_rtc(struct clocksource *cs)
>  {
> -	unsigned long offset;
> +	unsigned long offset, time;
> +	unsigned int cpu = get_cpu();
>  
>  	if (uv_get_min_hub_revision_id() == 1)
>  		offset = 0;
>  	else
> -		offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;
> +		offset = (uv_cpu_blade_processor_id(cpu) * L1_CACHE_BYTES) % PAGE_SIZE;
>  
> -	return (u64)uv_read_local_mmr(UVH_RTC | offset);
> +	time = (u64)uv_read_local_mmr(UVH_RTC | offset);
> +	put_cpu();
> +	return time;
>  }
>  
>  /*