linux-kernel - Re: [PATCH] mm: Fix kernel stack tagging for certain configs

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Message-ID: <92bfeeed-41b4-47f1-894d-ad003b4714b6@redhat.com>
Date: Thu, 4 Sep 2025 08:38:49 +0200
From: David Hildenbrand <david@...hat.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
 linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>, Kees Cook <kees@...nel.org>,
 kernel test robot <lkp@...el.com>, Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] mm: Fix kernel stack tagging for certain configs

On 03.09.25 20:12, Vishal Moola (Oracle) wrote:
> On Wed, Sep 03, 2025 at 09:46:44AM +0200, David Hildenbrand wrote:
>> On 02.09.25 22:06, Vishal Moola (Oracle) wrote:
>>> On Tue, Sep 02, 2025 at 08:23:06PM +0200, David Hildenbrand wrote:
>>>> On 02.09.25 19:59, Vishal Moola (Oracle) wrote:
>>>>> Commit 4ef905bda61f ("mm: tag kernel stack pages") began marking pages
>>>>> that were being used for the kernel stack.
>>>>>
>>>>> There are 3 cases where kernel pages are allocated for kernel stacks:
>>>>> CONFIG_VMAP_STACK, THREAD_SIZE >= PAGE_SIZE, THREAD_SIZE < PAGE_SIZE.
>>>>> These cases use vmalloc(), alloc_pages() and kmem_cache_alloc()
>>>>> respectively.
>>>>>
>>>>> In the first 2 cases, THREAD_SIZE / PAGE_SIZE will always be greater
>>>>> than 0, and pages are tagged as expected. In the third case,
>>>>> THREAD_SIZE / PAGE_SIZE evaluates to 0 and doesn't tag any pages at all.
>>>>> This meant that in those configs, the stack tagging was a no-op, and led
>>>>> to smatch build warnings.
>>>>>
>>>>> We definitely have at least 1 page we want tagged at this point, so fix
>>>>> it by using a do {} while loop instead of a for loop.
>>>>>
>>>>> Fixes: 4ef905bda61f ("mm: tag kernel stack pages")
>>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>>> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
>>>>> Closes: https://lore.kernel.org/r/202508300929.TrRovUMu-lkp@intel.com/
>>>>> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
>>>>> ---
>>>>
>>>> You sent the patch on August 20 and I replied on August 21.
>>>>
>>>> I did not receive any reply so far.
>>>
>>> Ah sorry, I didn't mean to miss your reply.
>>>
>>> I can't find your reply in my inboxes so I definitely missed it somehow.
>>> I'll go find it and respond.
>>
>> I had a mail server config issue on one day last month (sending @redhat.com
>> through kernel.org :) ), let me check if that was on that problematic day
>> and it might have went straight into your spam folder due to dkim mismatch.
>>
>> So the mailing list did not reject it:
>>
>> https://lore.kernel.org/all/96148baf-f008-449b-988b-ea4f07d18528@redhat.com/
>>
>> And yes, indeed, it was on that problemtic day, and there is:
>>
>> 	Received: from smtp.kernel.org
>>
>> So, problem on my side. Willy already replied, but let me resend that mail.
>>
>>>
>>>> And now I realize that this patch is not upstream yet and the commit id not
>>>> stable. So the Fixes/Closes etc. do not really apply.
>>>
>>> Gotcha.
>>
>> If there are bigger changes it usually makes sense to send a v2, or a simple
>> fixup as reply to the original patch (I prefer as inline reply).
> 
> Ok I'll keep that in mind for the future :). My mail client loves
> attaching the fixup patches as additional files, but I'll find a workflow
> for inlining them.

Oh, I really just format-patch, gedit to then copy and paste.

Just be careful if your mail client wraps at 80 chars as default. I have 
Thunderbird plugin where I can easily toggle that (Toggle Line Wrap).

-- 
Cheers

David / dhildenb