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

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Message-ID: <aLiFK8sIgbfiK-v2@fedora>
Date: Wed, 3 Sep 2025 11:12:59 -0700
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: David Hildenbrand <david@...hat.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 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.

> Of course, once it's in mm-stable or upstream, things get more tricky :)
> 
> -- 
> Cheers
> 
> David / dhildenb
>