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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-9087ff9d04csm13795626d6.3.2026.08.04.16.01.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Aug 2026 16:01:56 -0700 (PDT) Date: Tue, 4 Aug 2026 19:01:54 -0400 From: Gregory Price To: Matthew Wilcox Cc: Andrew Morton , Jane Chu , linux-mm@kvack.org, Muchun Song , Oscar Salvador , David Hildenbrand , Miaohe Lin , Naoya Horiguchi , Jan Kara , linux-fsdevel@vger.kernel.org, Christian Brauner , Jiaqi Yan Subject: Re: [PATCH v8 10/15] mm: Check individual hugetlb pages for poison Message-ID: References: <20260731200802.574821-1-willy@infradead.org> <20260731200802.574821-11-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: yc4pd65x3r47owcy5ysxgj8cfx65schc X-Rspamd-Queue-Id: A44EC20011 X-HE-Tag: 1785884518-24842 X-HE-Meta: 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 JMphMVAW xEc1vxAoh7o9is5zxfwLeaYnla0pSj7kNQ+RshjLdrZDh6Y1lY3M2vbQhoAclyZHQZbbnbYCZzv83vWR6XYQHD9aO2lX5v5J14vSMhYvu66DGv95aj3sxUnCnLSYEJ04GwXVz/uK/70M/MN7/xDACeJXU2lRLLTAsyPwH+eV8c7Mge39G3p8XW+mRBNVL9auAkogCY9wSHYagNt2SPsWHHFuF9x6cWVgN7w3lMy8gMt3bKlzymjcjfnr5pihT1Yswzj+0N50vSxNe4u9ZMthfglIzyVz/nMKD52ENaazg8RZCp7ZQ6ZRv5PPVtgwkMJJsNjD0yjhuJcNWv/QRkmNW09J5pmyACZl+d86WE4PrqGujyAObBhJf9LTIY7yKXqYD3SQxi/ULDBVw/RdspK1wyUlb/A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 04, 2026 at 10:21:29PM +0100, Matthew Wilcox wrote: > On Tue, Aug 04, 2026 at 03:15:37PM -0400, Gregory Price wrote: > > So the pointer we get back from page_folio() must have been a folio _at > some point_. It may not be a folio now. It may be a folio, but not one > that contains this page. But it's not a wild pointer, and treating it > as if it's a folio won't cause any harm (as long as we're really careful). > > Specifically, we call: > > > + if (!folio_test_huge_poison(folio)) { > > and all that does is access folio->page.page_type aka mapcount. So if > the pointer we have is not a current folio, it'll just return false and > we'll check PageHWPoison. > > So the only case this can return 'true' is if the folio was hugetlb > at that exact point. And we've got the hugetlb lock, so it can't stop > being a hugetlb folio. At this point it's safe to walk the list. > This is basically the reasoning i came to, ergo "not worth addressing" > That's my reasoning, and I think Sashiko has explained enough of its > reasoning to be fairly sure Sashiko is wrong about this. But hey, > you're not Sashiko. Maybe you've found a gap in my logic. I think sashiko is essentially just saying: "But if someone does a dumb thing with this interface in the future dumb things will happen" To which we say "Don't do the blatantly dumb thing :]" ~Gregory