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

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Message-ID: <902b4745-4ca0-9b29-6563-ed49f924a5e1@intel.com>
Date:   Thu, 26 May 2022 08:30:21 -0700
From:   Dave Hansen <dave.hansen@...el.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

On 5/20/22 13:37, Mike Travis wrote:
> To avoid a "BUG: using smp_processor_id() in preemptible" debug
> warning message, disable preemption around use of the processor id.

I'm sure this gets rid of the warning.  But, could you please take a
quick look at the callers and ensure that they can handle if this read
comes from another CPU?

In other words, what would actually go wrong if uv_read_rtc() got
preempted in this region?  What would this actually fix?