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[67.164.59.41]) by smtp.googlemail.com with ESMTPSA id d9443c01a7336-24a92f89809sm98463435ad.2.2025.09.02.10.59.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Sep 2025 10:59:33 -0700 (PDT) From: "Vishal Moola (Oracle)" To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Kees Cook , "Vishal Moola (Oracle)" , kernel test robot , Dan Carpenter Subject: [PATCH] mm: Fix kernel stack tagging for certain configs Date: Tue, 2 Sep 2025 10:59:03 -0700 Message-ID: <20250902175903.1124555-1-vishal.moola@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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) --- kernel/fork.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 1b394426ab4a..9b13cb83e1c6 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -448,14 +448,15 @@ static void account_kernel_stack(struct task_struct *tsk, int account) } else { void *stack = task_stack_page(tsk); struct page *page = virt_to_head_page(stack); - int i; + int i = 0; /* All stack pages are in the same node. */ mod_lruvec_kmem_state(stack, NR_KERNEL_STACK_KB, account * (THREAD_SIZE / 1024)); - for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++, page++) - __SetPageStack(page); + do { + __SetPageStack(page++); + } while (++i < THREAD_SIZE / PAGE_SIZE); } } @@ -474,10 +475,11 @@ void exit_task_stack_account(struct task_struct *tsk) } } else { struct page *page = virt_to_head_page(task_stack_page(tsk)); - int i; + int i = 0; - for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++, page++) - __ClearPageStack(page); + do { + __ClearPageStack(page++); + } while (++i < THREAD_SIZE / PAGE_SIZE); } } -- 2.51.0