linux-kernel - Re: [PATCH] x86,mm: print likely CPU at segfault time

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Date:   Wed, 21 Jul 2021 22:36:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, kernel-team@...com,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Subject: Re: [PATCH] x86,mm: print likely CPU at segfault time

Rik,

On Mon, Jul 19 2021 at 15:00, Rik van Riel wrote:
>
> Adding a printk to show_signal_msg() achieves that purpose. It isn't
> perfect since the task might get rescheduled on another CPU between
> when the fault hit and when the message is printed, but it should be
> good enough to show correlation between userspace and kernel errors
> when dealing with a bad CPU.

we could collect the cpu number in do_*_addr_fault() before interrupts
are enabled and just hand it through. There are only a few callchains
which end up in __bad_area_nosemaphore().

Thanks,

        tglx