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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4601f35133csm62850063f8f.25.2026.06.09.13.24.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jun 2026 13:24:22 -0700 (PDT) Date: Tue, 9 Jun 2026 16:24:17 -0400 From: "Michael S. Tsirkin" To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Miaohe Lin , "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Muchun Song , Oscar Salvador , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli , Naoya Horiguchi Subject: Re: [PATCH splitout] mm: memory-failure: serialize TestSetPageHWPoison with zone->lock Message-ID: <20260609161227-mutt-send-email-mst@kernel.org> References: <20260609111020.e88f51a7b6ebc37360d66fdc@linux-foundation.org> MIME-Version: 1.0 In-Reply-To: <20260609111020.e88f51a7b6ebc37360d66fdc@linux-foundation.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Jnd6yT_rMM2CxZN1VdynhMlVmMe1vq-J6Bl5iArE3TQ_1781036664 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: EF72DC0009 X-Stat-Signature: bmt3jx3spp1hi4gegc9eo3j85a8ku4kt X-HE-Tag: 1781036667-482100 X-HE-Meta: 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 +O6whQGg btY7Hqg5WHKv9Tbcfu7/FlUw16+4TQktf8ctOh6+YF6/uSeI6vWM6nYAVyaQ0Fzr+akhJJPyl7YF5/hAez8xcOKxH2BKIfLhtEGCZN260eD0UiwsaDuyAWO1GOjK0DwZ9hmmJe8EY5aBXlsZ2rGx2jtn2d7ZUILDff3Brr+hY1Xs2xCf4AVU9QDzQviGBVj7HzCt7EQucjtF7RRl7ZUfQLzaf5Z1OlBICaHgg+dIEZ95Ttas9D0bof2gdUM2ZMnw69n5LiCnUsxaeBdKpajAQwAUFXXKpuyoWTBYzpHYwmaS6oKgrkTir7/6aRUqLHiuiBHFuj6bkNkz9B4Y9JhDQM7wr+wqC/QLIjZIMer+Di7Xs7lRN6WwLrmUD9z+h/kdMumqwKYnjjBucPUaP0QobL55WhRN1WjyNCdTFvMuds2j2mzhlOQuneXv3NtGrytl+gO7ObtZhrsonMuE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 09, 2026 at 11:10:20AM -0700, Andrew Morton wrote: > On Tue, 9 Jun 2026 06:12:49 -0400 "Michael S. Tsirkin" wrote: > > > TestSetPageHWPoison() is called without zone->lock, so its atomic > > update to page->flags can race with non-atomic flag operations > > that run under zone->lock in the buddy allocator. > > > > In particular, __free_pages_prepare() does: > > > > page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; > > > > This non-atomic read-modify-write, while correctly excluding > > __PG_HWPOISON from the mask, can still lose a concurrent > > TestSetPageHWPoison if the read happens before the poison bit > > is set and the write happens after. Will only get worse if/when > > we add more non-atomic flag operations. > > > > Fix by acquiring zone->lock around TestSetPageHWPoison and > > around ClearPageHWPoison in the retry path. This > > serializes with all buddy flag manipulation. The cost is > > negligible: one lock/unlock in an extremely rare path > > (hardware memory errors). > > > > Note: SetPageHWPoison and TestClearPageHWPoison calls elsewhere > > in this file operate on pages already removed from the buddy > > allocator or on non-buddy pages (DAX, hugetlb), so they do not > > need zone->lock protection. > > Sashiko is saying this doesn't do anything "Because > __free_pages_prepare() executes entirely locklessly". Did it goof? > > https://sashiko.dev/#/patchset/df06b66fe4ff8e925ee0714955abc2183a727b90.1780998980.git.mst@redhat.com > Oh. So it only helps with the prezero patches. Maybe other places where flags are touched locklessly. Not __free_pages_prepare. I was too focused on that. Scrap this please. I'll try to think of something. -- MST