linux-kernel - Re: [PATCH 2/3] mm: page table check

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Date:   Sat, 27 Nov 2021 14:48:00 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Fusion Future <qydwhotmail@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Paul Turner <pjt@...gle.com>, weixugc@...gle.com,
        Greg Thelen <gthelen@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>, masahiroy@...nel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        frederic@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH 2/3] mm: page table check

On Sat, Nov 27, 2021 at 3:41 AM Fusion Future <qydwhotmail@...il.com> wrote:
>
> It seems after updating to linux-next-20211125, my system is crashing
> frequently due to "kernel BUG at mm/page_table_check.c:101".

Thank you for reporting this issue:

 99                 if (anon) {
100                         BUG_ON(atomic_read(&ptc->file_map_count));
101                         BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0);

This BUG_ON checks that during unmap anon map counter (cleared in
ptep_clear_flush()) does not become negative. If it becomes negative
it means that we missed accounting for this anon mapping during
set_pte(). Is there a config and environment that I could use to repro
this problem?

Thank you,
Pasha