linux-kernel - Re: [PATCH] x86: mce: always use 64-bit timestamps

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Message-ID: <20180618125106.GB24921@zn.tnic>
Date:   Mon, 18 Jun 2018 14:51:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Tony Luck <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        y2038@...ts.linaro.org, "H. Peter Anvin" <hpa@...or.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: mce: always use 64-bit timestamps

On Mon, Jun 18, 2018 at 12:06:46PM +0200, Arnd Bergmann wrote:
> The machine check timestamp uses get_seconds(), which returns an 'unsigned long'
> number that might overflow on 32-bit architectures (in the distant future)
> and is therefore deprecated.
> 
> The normal replacement would be ktime_get_real_seconds(), but that needs to
> use a sequence lock that might cause a deadlock if the mce happens at just
> the wrong moment. The __ktime_get_real_seconds() skips that lock and is
> safer here, but has a miniscule risk of returning the wrong time when we read
> it on a 32-bit architecture at the same time as updating the epoch, i.e.
> from before y2106 overflow time to after, or vice versa.
> 
> This seems to be an acceptable risk in this particular case, and is the
> same thing we do in kdb.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/x86/kernel/cpu/mcheck/mce.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Applied, thanks.

-- 
Regards/Gruss,
    Boris.

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