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Tue, 03 Nov 2026 10:27:50 -0800 (PST) Date: Tue, 3 Nov 2026 13:27:48 -0500 From: Johannes Weiner To: "Vlastimil Babka (SUSE)" Cc: "Gregory Price (Meta)" , Zi Yan , Shakeel Butt , Mike Rapoport , David Hildenbrand , Oscar Salvador , "Matthew Wilcox (Oracle)" , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josef Bacik , stable@vger.kernel.org Subject: Re: [PATCH v2 1/5] mm/page_alloc: clear ->private of deferred free pages Message-ID: References: <20261103-pgalloc-ai-hotfixes-v2-0-e0d2890ab74f@kernel.org> <20261103-pgalloc-ai-hotfixes-v2-1-e0d2890ab74f@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261103-pgalloc-ai-hotfixes-v2-1-e0d2890ab74f@kernel.org> X-Rspamd-Server: rspam12 X-Rspam-User: X-Stat-Signature: fo3bux9hs1cyydsazwests1a8perwfch X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 5AD4E180003 X-HE-Tag: 1793730473-37386 X-HE-Meta: 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 OonXvSLL 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Nov 03, 2026 at 05:16:47PM +0100, Vlastimil Babka (SUSE) wrote: > From: Josef Bacik > > free_pages_nolock() and free_frozen_pages_nolock() put the page on > zone->trylock_free_pages if they get neither the pcp lock nor zone->lock. > add_page_to_zone_llist() keeps the order of the page in page->private. > The next free_one_page() which does get zone->lock passes these pages to > split_large_buddy() with ->private still set. > > __free_one_page() writes ->private of the head of the resulting free page > only. If the deferred page is merged with its lower buddy, it becomes a > tail of that free page and keeps the order in ->private. > > All other free pages which are not the head of a buddy have a ->private > of zero, and since commit 819bfbd47e49 ("mm/page_alloc: remove > set_page_private() in prep_compound_tail()") the allocator relies on it. > When the stale page is allocated again as a tail of a larger page: > > - prep_compound_tail() hits VM_WARN_ON_ONCE(tail->private); > - with the page checks enabled, __free_pages_prepare() reports > "BUG: Bad page state", "nonzero private", and leaks the whole page; > - without them the value is seen by whoever uses that page next, e.g. as > folio->private of a folio which is split off a large folio. > > Only pages of an order above zero are affected. Those can be freed > through _nolock() by the stack depot (order 2) and by SLUB (a new slab > which cannot be added to the partial list by kmalloc_nolock()). > > Clear ->private when the page is taken off the list. > > Fixes: 8c57b687e833 ("mm, bpf: Introduce free_pages_nolock()") > Cc: > Assisted-by: LLM > Signed-off-by: Josef Bacik > Signed-off-by: David Hildenbrand (Arm) > Reviewed-by: Zi Yan > Signed-off-by: Vlastimil Babka (SUSE) Reviewed-by: Johannes Weiner