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Fri, 16 Oct 2026 15:35:50 -0700 (PDT) Received: from [2a00:79e0:2eb4:9:17ee:cb47:3ad4:ee3c] ([2a00:79e0:2eb4:9:17ee:cb47:3ad4:ee3c]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3acc98139ccsm3148060a91.0.2026.10.16.15.35.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Oct 2026 15:35:49 -0700 (PDT) Date: Fri, 16 Oct 2026 15:35:48 -0700 (PDT) From: David Rientjes To: Karl Mehltretter cc: Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , Roman Gushchin , Shengming Hu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/slub: initialize the free pointer of the bootstrap kmem_cache_node In-Reply-To: <20261010203906.93156-1-kmehltretter@gmail.com> Message-ID: <3284bb03-6c23-611c-872c-19954a7f3381@google.com> References: <20261010203906.93156-1-kmehltretter@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 On Sat, 10 Oct 2026, Karl Mehltretter wrote: > With slub_debug=FZPU, validating kmem_cache_node reports > > BUG kmem_cache_node (Not tainted): Freepointer corrupt > Object 0xffff888000140040 @offset=64 fp=0x5a5a5a5a5a5a5a5a > > and taints the kernel. Poisoning places the bootstrap object's free > pointer outside the object, where check_object() checks it even while > allocated. > > early_kmem_cache_node_alloc() previously took this object from a > freelist with an initialized pointer. It now takes it from the slab > iterator and builds the freelist only for the remaining objects, > leaving its pointer filled with POISON_INUSE. > > Initialize the bootstrap object's free pointer to NULL. > > Fixes: dc795d4c0282 ("mm/slub: defer freelist construction until after bulk allocation from a new slab") > Assisted-by: LLM > Signed-off-by: Karl Mehltretter Tested-by: David Rientjes