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b=1ooxQzN1/Iis7wo4qiD0UQM20Iq0wgdIB/2Da6G96vQezHcr2GL1PY8otynXf4F/m Zoyo5eezro3XDif4O45Ll5elF47hRGsxQTfydbJr6YHQenjtHLrTy/RFznmw/1il2u jrr67O1j2x2g829K+t8kiKwhd/QkYrxyzlzEmTIs= Date: Fri, 28 Aug 2026 18:38:01 -0700 From: Andrew Morton To: James Houghton Cc: Lance Yang , David Hildenbrand , Lorenzo Stoakes , Zi Yan , Baolin Wang , liam@infradead.org, Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Yang Shi , zokeefe@google.com, hughd@google.com, Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/khugepaged: Don't install PMDs in uffd-minor-registered VMAs Message-Id: <20260828183801.04fd2d2a6af837cb45b60e0f@linux-foundation.org> In-Reply-To: References: <20260828222640.1638457-1-jthoughton@google.com> <20260828173302.29778f1bf802a1db932778ad@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=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: rtzib9ndymtqq4tfqkc1cafi3w1awn9k X-Rspamd-Queue-Id: D795440005 X-HE-Tag: 1787967483-862816 X-HE-Meta: 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 gJttCyGo 1mzZt6UvugfOOXsAumaQWEpGQchCpecMQhlZz+xrfnjLBSntvm4pcCP0PBL74JSfE80dJLCsxozy1+ARyL4zI0905K19v2eYOUI8EUqGjfExEaja6Vz/C689OseL9CX+cwaqujIqCrjHFGviPt/Y19XpvfhLxhgQ6+pPGu/soFX8kRXQFPRDMsGyE5QoV/Gi7qpa2sHgnBT70I/RDqxW4IcpsHdUe7TkdbSBfZnqLCN9hUVUjJdIrVye1XO8oxBFFSb5k61zUWHBtmy+a9A+/jpplr7h6TBNHkNTynnb/uAE/ghYWXbMiXnzfyolQ5I6Zh1v94LQvrdtRcxmywxZZVVQWpFRfnaMDtg6ZXdB5FloUwK6BCUjnvWthL/xUq0Lg8hso Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 28 Aug 2026 18:18:11 -0700 James Houghton wrote: > On Fri, Aug 28, 2026 at 6:09 PM James Houghton wrote: > > > > On Fri, Aug 28, 2026 at 5:33 PM Andrew Morton wrote: > > > Wondering what Lance tested. Was he able to reproduce the bug? > > > > I assume he just re-ran my repro, but yeah I'm not sure, heh. Lance, > > what did you test? > > Ah, just to be clear, I linked a repro on v1. Here[1] is that repro. > Sorry, slipped my mind to also include it in the notes for this v2. > > [1] https://gist.github.com/48ca/d399bf534158e80241fb4937ef1ff664 Cool thanks, I'll slap this into the changelog. # ./a.out TAP version 13 1..1 madvise(MADV_COLLAPSE) succeeded ioctl(UFFDIO_CONTINUE) failed: File exists (errno=17) not ok 1 - memfd userfaultfd MINOR continue test We do have a ton of uffd selftesting code in there. Adding this case to uffd-unit-tests.c would presumably be pretty simple. We don't really have a policy on adding a test-case after fixing something - it's common practice but why? We already fixed it!