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Received: from 30.74.144.118(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X6GuTEm_1783041530 cluster:ay36) by smtp.aliyun-inc.com; Fri, 03 Jul 2026 09:18:50 +0800 Message-ID: <918c72ae-dd3a-41e9-84ca-164f2e0e6d01@linux.alibaba.com> Date: Fri, 3 Jul 2026 09:18:49 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/huge_memory: set PG_has_hwpoisoned only after new folio head is established To: Rik van Riel , linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, ziy@nvidia.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, yang@os.amperecomputing.com, stable@vger.kernel.org References: <20260701174235.3173401-1-riel@surriel.com> From: Baolin Wang In-Reply-To: <20260701174235.3173401-1-riel@surriel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: oddaffthkcy57xraiscnuubnt1q4w9kw X-Rspam-User: X-Rspamd-Queue-Id: BB3B1C0004 X-Rspamd-Server: rspam05 X-HE-Tag: 1783041535-773157 X-HE-Meta: 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 v7TCYYTd w5ptygnImlhMYHs1+FIg6qx79bXFwGyIIqr/EKneEg79/tgDCSQMiFbi2zHJYdRch2Y9PrJTIlB2V7FzZpm/aoTbNbXxsimXNJA5K5o+fqhh71aemUATMAx9iYVnPx/c6aLRnNCRlaxSA5CEL3MaPjIue4zkpZplL3NitNCQrqqh5BPWg+bXU+ds/iXqT2AUvKrV0g0ZSF/yBXYjxduYZN/bb68HgerGDe2rNZ8CcUcg/4jf3nt/HQYqZF13ZOi2CWE0LOIy2Xc9oAeQjC1UWZMn039NOlTds4EQD1PyH1T6jrMlnCJSdlmn44AvOw263WIxoGgbzuvJFur6naDTZv2QZD0KH30SQy6rzlcSM832PnLmOBLVLwp5CLGIaXp27RzhDr9k5XJPV0kxoutWcwezANdmXl18dBEwABjRm56SZkxL5GRLzKXdYX9OmQPXWpTW4mRPu/Xh6rsc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/2/26 1:42 AM, Rik van Riel wrote: > __split_folio_to_order() copies the hwpoison state onto each new > sub-folio while splitting a folio to a non-zero order. It does so via > > if (handle_hwpoison && page_range_has_hwpoisoned(new_head, new_nr_pages)) > folio_set_has_hwpoisoned(new_folio); > > *before* clear_compound_head(new_head)/prep_compound_page(new_head, ...) > turns @new_head from a tail page into a proper folio head. > > PG_has_hwpoisoned is a FOLIO_SECOND_PAGE flag, so folio_set_has_hwpoisoned() > resolves to folio_flags(folio, 1). With the new compound_info-based > page-flags layout, folio_flags() asserts the page is not a tail: > > VM_BUG_ON_PGFLAGS(page->compound_info & 1, page); > VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page); > > At the current call site @new_head still has the tail marker > (compound_info bit 0 set, PG_head clear), so on CONFIG_DEBUG_VM kernels > this hits: > > kernel BUG at include/linux/page-flags.h:354 > folio_flags+0x82 > folio_set_has_hwpoisoned > __split_folio_to_order > __split_unmapped_folio > __folio_split > truncate_inode_partial_folio (shmem hole-punch / MADV_REMOVE) > > Reproduced by syzkaller: hwpoison-inject a few subpages of a large shmem > folio, then MADV_REMOVE (fallocate punch hole) on the same range, which > splits the partial folio to a non-zero order. > > memory_failure() tries to split the poisoned folio to order 0 first, but > that split is best-effort; when it fails the folio is left large with > PG_has_hwpoisoned set, the case fa5a06170036 added this hwpoison copying > for. > > Move the folio_set_has_hwpoisoned() call to after > clear_compound_head()/prep_compound_page(), where @new_folio is a real > order-new_order head folio (handle_hwpoison implies new_order != 0, so a > second page always exists). The flag still lands on the same struct page > (page[1] of the new folio); only the ordering relative to compound-head > setup changes, satisfying the FOLIO_SECOND_PAGE precondition. > > Fixes: fa5a06170036 ("mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order") > Signed-off-by: Rik van Riel > Assisted-by: Claude:claude-opus-4-8 > Reviewed-by: Zi Yan > Acked-by: David Hildenbrand (Arm) > Tested-by: Lance Yang > Cc: stable@vger.kernel.org > --- Good catch. LGTM. Reviewed-by: Baolin Wang