linux-kernel - Re: [BUG] WARNING: CPU: 3 PID: 1 at mm/debug_vm

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Message-ID: <CAHk-=wg6fw130AkO72GPFow9PHvP9odnC5LZ0UaY9bJQuF-C5A@mail.gmail.com>
Date:   Tue, 12 Oct 2021 12:15:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Gavin Shan <gshan@...hat.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [BUG] WARNING: CPU: 3 PID: 1 at mm/debug_vm_pgtable.c:493

On Tue, Oct 12, 2021 at 11:55 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
>
> I saved off that warning from a different branch, and looking at the dmesg,
> it is:
>
>   Linux version 5.14.0-rc2-test+
>
> Which shows this happened on 5.14 as well (and explains why the line
> numbers are different).

Ok, yes, that's the exact same "pud_set_huge()" failure.

So it's the same issue, and has been going on for a while, and
presumably very few people end up enabling DEBUG_VM_PGTABLE (together
with it being hard to trigger).

Or it's something specific to your setup, but that sounds unlikely.

You might add some debugging to the x86 pud_set_huge() function,
something like the attached (obviously entirely untested) patch.

           Linus

View attachment "patch.diff" of type "text/x-patch" (904 bytes)