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

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Message-ID: <f41383c3-913a-489a-82e6-d2c8d5519eed@redhat.com>
Date: Tue, 2 Sep 2025 20:23:06 +0200
From: David Hildenbrand <david@...hat.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: 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 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.

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.

My current opinion is that we don't want this. (see vmalloc reasoning 
and unclear use)

I'm happy to be convinced otherwise.

-- 
Cheers

David / dhildenb