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charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: ko1wz7kajdge58xabaue3j5a6oh3m7j1 X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C5607100005 X-Rspam-User: X-HE-Tag: 1793103213-210022 X-HE-Meta: U2FsdGVkX1+4+lviDqhxAg9+JbCT5JU9uNKkgQakmY2nkjT9yuv1QqqykDr5LuKUTrtWQuGF23r80yRu2FXUft5ITA64RctzUeNmD0+BIxx5X/TIRQcmIfgrKN0OAbxLDAYlD6dongh42VyHjtLTRIUhoQvUfKj6eqLCSsuu9JxOlPTPGyDeR7rTfYY/y9vclTpqzPIfHJ90pEjJak7VM3EStKbu45dOPlJgv78OHtDfjdS8sQIu4fk1WUyr6/ay5COzR2ejrdsKgCmkLSP2Xh1OpGB/Xpz0U6orp1G1Muw3nD1JJGh5RMiZFV411Z5hsy2j0gc/VUa9j585Txq229+rjGCM6+CcYw1AtBfCKpkvnwxJYLzbd7FCwbGZ8zgTN0wplrYl5yES9tfgCcNiwAjuZoEGLDvVh4p9KqIvrFodWLx0J5FkBlL3nefgxqvUuvdnHl7Yim1pLolwz2b/JsmH0sDuYahD/IWdmJAVyxfDGvhSGJ1WYSi5LiFHDRHBBp5FuH5gKM3EXVojiCFqKJsQS9ET2bwPZzFD3+YbzdVP0mH6y70e8V5Zao2qypq8E/Au0at4Z51tUp7VIfTIAlj32vbzZyC7bwhgZkbueeiwMxZBoD/11Tor0/4y34v2tYEvRA0wHtAi/hO9neOXJzZ/1Y9n07uJrVCF+joDNqWcEs3EfLgBaGAnN41Qso+w4ba8WolwZNw3QsrfnipC/6B11JJw1aHMZgPBUBUtBjgi44ab56YKsb/VTz/DbaRy+Y1KtDt/a9OYqe3K/9IRifiz4Zq4PzJCOujyGdNiMNTwtPvtpwYMlyjoXW6lyssOZxgPeskSrIigti6I0B0JKRWus6MvIAYBWRQYh3f6//x/i3gv6NqFJPjAul0wkDTG3kLJQZq55ftvUXxJxAEmumTOvoFC3/LG5On+AAe5EGUSG4ThlCsDeOcmMVqFPsbQ70Cq2f2Y3vSyLHJXaiJ E+zfJi+c XyX03Dm2JqfDkEUo2ky3W6gdxQyehYyg6cZZv2/w/sgyNY3sklh3GEQhUcf3FLTSqCP3THmjg8FEa4RjgAGRYdBIvLr24x+lJP4NWUYSsAHI0xugjlrFhl3xrOtuarHHjOw6ylTJXQMffzk6wiPpEzU6h0etqdUQG53Lek9oERAYhNahIeJbThIFzyM0rKfQKrKDLhH15bXK6xjk= 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 On Tue, Oct 27, 2026 at 12:00:47PM +0000, Kiryl Shutsemau wrote: > Fair enough. Here's some context. > > HVO (HugeTLB Vmemmap Optimization) frees most of the memmap of a hugetlb > folio by remapping the struct pages after the first vmemmap page to a > shared page, mapped read-only. > > Every lockless get of a page reference (e.g. page cache lookup, PFN > scanners) relies on page_ref_add_unless_zero(), which is > atomic_add_unless(&page->_refcount, nr, 0). > > The page can be freed and reused between finding it and the get; the > zero refcount is what makes the get fail. The race: > > lockless get other CPU > c = atomic_read(&page->_refcount) > c != 0 > page freed > page allocated as a hugetlb tail > HVO remaps it read-only > try_cmpxchg(&page->_refcount, &c, c + nr) > -> write fault on read-only vmemmap I missed a little something here; page->_refcount is in the page-frame; how does the page itself being RO affect this?