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[67.164.59.41]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-24b0e860ab5sm32663555ad.5.2025.09.02.13.06.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Sep 2025 13:06:07 -0700 (PDT) Date: Tue, 2 Sep 2025 13:06:05 -0700 From: "Vishal Moola (Oracle)" To: David Hildenbrand Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Kees Cook , kernel test robot , Dan Carpenter Subject: Re: [PATCH] mm: Fix kernel stack tagging for certain configs Message-ID: References: <20250902175903.1124555-1-vishal.moola@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 > > Reported-by: Dan Carpenter > > Closes: https://lore.kernel.org/r/202508300929.TrRovUMu-lkp@intel.com/ > > Signed-off-by: Vishal Moola (Oracle) > > --- > > 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. > 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. > 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 >