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b=1PMqZBSLrP+eQgLFj2LF6Ah+EcVk6F+3MasY6U2Od4G5bTBhHptzqIdM2bQK5amdH sR1fj+9hS+/8dgC6mygfrZ75rGcEd/0lYAIcOlUfqmxSleAhT5V1CMTOf3kabUKUKd ed+kJmrv2aGKw5PcIo5j404MUFiIFaBC67gOhdIg= Date: Thu, 19 Mar 2026 19:31:57 -0700 From: Andrew Morton To: Jinjiang Tu Cc: , , , , , , , , , , , Subject: Re: [PATCH v3] mm/huge_memory: fix folio isn't locked in softleaf_to_folio() Message-Id: <20260319193157.7cacc7b6628e94ff62541c34@linux-foundation.org> In-Reply-To: References: <20260319012541.4158561-1-tujinjiang@huawei.com> <20260319155101.f7a62c04a7bcfc838b63824c@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5684CC0003 X-Stat-Signature: zgkdte3ubhjqzr5nqigfh79z1ppbzz95 X-Rspam-User: X-HE-Tag: 1773973919-335360 X-HE-Meta: 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 zkB33nVs CYoBD Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 20 Mar 2026 09:52:42 +0800 Jinjiang Tu wrote: > >> In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages > >> are visible before the tail page becomes non-compound. smp_wmb() should > >> be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a > >> result, if zap_nonpresent_ptes() accesses migration entry that stores > >> tail pfn, softleaf_to_folio() may see the updated compound_head of tail > >> page before page->flags. > > Please describe the userspace-visible runtime effects of this bug. > > This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio(). > > This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further swapops predicates"), > which in merged in v6.19-rc1. Great, thanks, I added cc:stable.