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

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Message-ID: <b0ed22cd-ebf9-41f7-b5fb-6fb078db593e@redhat.com>
Date: Wed, 3 Sep 2025 09:46:44 +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 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).

Of course, once it's in mm-stable or upstream, things get more tricky :)

-- 
Cheers

David / dhildenb