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b=Tdms6Q4UWHlY9evtVY26SY666VGRVDiqz6LOSvJc2XVieo0g+lhSmUBzTmQK0fXOd fs8FcsZXidCPiB/D47lmDgTEmthu55EQ0+xL56qqscDdUNxWCa93gezbvp9vf75HvF HkNBU/0CnHTwEJpCZIyk5tdQjzaya3iUdUungReDLqKAuhBSqcrxk/7b7zbO/BBZSS 7n4Lv5ORNf/E884FHGRmdnjAlQpXXBRgEczHwZT9DMJ08BHBaBZs1OncwCXzIlMckR hBHQT0JXJ9eIpkJYyVXE6M3ofBob9vMk+lNYjZmX7PsWxu3R4WaZ6bF+GWGsOiqeDD fhTKu5jfv4cxQ== From: "Vlastimil Babka (SUSE)" Date: Tue, 03 Nov 2026 17:16:51 +0100 Subject: [PATCH v2 5/5] mm/page_alloc: remove the zone_spans_pfn() check from get_pfnblock_bitmap_bitidx() X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261103-pgalloc-ai-hotfixes-v2-5-e0d2890ab74f@kernel.org> References: <20261103-pgalloc-ai-hotfixes-v2-0-e0d2890ab74f@kernel.org> In-Reply-To: <20261103-pgalloc-ai-hotfixes-v2-0-e0d2890ab74f@kernel.org> To: Johannes Weiner , "Gregory Price (Meta)" , Zi Yan , Shakeel Butt , Mike Rapoport , David Hildenbrand , Oscar Salvador , "Matthew Wilcox (Oracle)" Cc: Suren Baghdasaryan , Michal Hocko , Brendan Jackman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Vlastimil Babka (SUSE)" , Josef Bacik , stable@vger.kernel.org X-Mailer: b4 0.16.0 X-Stat-Signature: 6p1wc4yxkbcqp3au8si76e4ts91judg4 X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: E694D40007 X-HE-Tag: 1793722632-230736 X-HE-Meta: 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 QgwjDXjT zezG9aAHkLQdzbcp1DTHIwRlcp12i5DI2Vv/geIKaGkmHyh+A2k+n2szDEqYyPoD37VuDMYrwNlHFdjpRj5lWJH1nP22+50lU68Cp6R729HU+z1uFGtsBPQkETqLIJPaGfD8uedFJlawot0vBhUBd1kXhZy7QoxQOKAl1UStJFvXT3+iZLlRmBkIFYvrUFd6yY5iTcCaqYxTjZAtEpcpWj7YqAMVTWCbkpEfnWi+fQ4b2XpIm3C1rSt4oY1qzQShEQXfohgF1GqPCQ9G/cZQdR3vyGDP2OTkdr3e95QpNyrv2T0IAwUo19fBjG15ecddjd8OIXAUrS5MkAjRDOXd7EyWraLC2y5Khn0No 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 Whenever the flags of a pageblock are read or written, a kernel with CONFIG_DEBUG_VM makes sure that the pfn lies within the zone of the page. Unlike bad_range(), that check reads zone->zone_start_pfn and zone->spanned_pages without zone->span_seqlock. Memory hotplug changes the two fields one after the other. If the lower end of a zone moves, the zone seems to end before its last pages in between. A page of that part which is freed at that moment, on another CPU, ends in page dumped because: VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn)) kernel BUG at mm/page_alloc.c:372! free_unref_folios+0x55e/0xed0 folios_put_refs+0x2b5/0x530 An attempt has been made [1] to fix this with the span seqlock check. But that can trigger all sorts of problems in restricted contexts, as noted by sashiko [2]. Since this is just a sanity debug check and anything with BUG_ON is frowned upon anyway, just remove it altogether. Reported-by: Josef Bacik Closes: https://lore.kernel.org/all/20261027-pgalloc-ai-hotfixes-v1-9-9c7d1aca801e@kernel.org/ [1] Link: https://lore.kernel.org/all/sashiko-outbox-188081@kernel.org/ [2] Fixes: 86051ca5eaf5 ("mm: fix usemap initialization") Cc: Signed-off-by: Vlastimil Babka (SUSE) --- mm/page_alloc.c | 1 - 1 file changed, 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 41fd80c0c762..3a7b9b533368 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -370,7 +370,6 @@ get_pfnblock_bitmap_bitidx(const struct page *page, unsigned long pfn, BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4); #endif BUILD_BUG_ON(__MIGRATE_TYPE_END > PAGEBLOCK_MIGRATETYPE_MASK); - VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); bitmap = get_pageblock_bitmap(page, pfn); *bitidx = pfn_to_bitidx(page, pfn); -- 2.56.0