linux-kernel - Re: [PATCH] mm: add stack trace when bad rss-counter state is detected

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Message-ID: <5cdd3e44-3e3c-4697-905a-ecc61093f7bc@163.com>
Date: Wed, 23 Jul 2025 17:10:31 +0800
From: Xuanye Liu <liuqiye2025@....com>
To: David Hildenbrand <david@...hat.com>, Kees Cook <kees@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: add stack trace when bad rss-counter state is
 detected

在 2025/7/23 16:42, David Hildenbrand 写道:
> On 23.07.25 10:05, David Hildenbrand wrote:
>> On 23.07.25 09:45, Xuanye Liu wrote:
>>>
>>> 在 2025/7/23 15:31, Kees Cook 写道:
>>>> On Wed, Jul 23, 2025 at 03:23:49PM +0800, Xuanye Liu wrote:
>>>>> The check_mm() function verifies the correctness of rss counters in
>>>>> struct mm_struct. Currently, it only prints an alert when a bad
>>>>> rss-counter state is detected, but lacks sufficient context for
>>>>> debugging.
>>>>>
>>>>> This patch adds a dump_stack() call to provide a stack trace when
>>>>> the rss-counter state is invalid. This helps developers identify
>>>>> where the corrupted mm_struct is being checked and trace the
>>>>> underlying cause of the inconsistency.
>>>> Why not just convert the pr_alert to a WARN?
>>> Good idea! I'll gather more feedback from others and then update to v2.
>>
>> Makes sense to me.
>
> After discussion this with Lorenzo off-list, isn't the stack completely misleading/useless in that case?
>
> Whatever caused the RSS counter mismatch (e.g., unmapped the wrong pages, missed to unmap pages) quite possibly happened in different context, way way earlier.
>
> Why would you think the stack trace would be of any value when destroying an MM (__mmdrop)?
>
> Having that said, I really hate these "pr_*("BUG: ...") with passion. Probably we'd want to invoke the panic_on_warn machinery, because something unexpected happened.
>
The stack trace dumped here may indeed not reflect the root cause ——
the actual error could have occurred much earlier, for example during a
failed or missing page map/unmap operation.
The current stack (e.g., in __mmdrop() or exit_mmap()) is merely part
of the cleanup phase.

Given that, how should we go about identifying the root cause when such an issue occurs?

Is there any existing way to trace it more effectively, or could we introduce a new mechanism
to monitor and detect these inconsistencies earlier?                                         

Let’s brainstorm possible solutions together.

-- 
Thanks,
Xuanye