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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Andrew Morton , David Hildenbrand , Yuan-Hao Hsu Subject: Re: [PATCH v3 2/6] mm: gup: clarify a reason to check pte/pmd in gup_fast_pte_range() Message-ID: References: <20261109-refactor_gup_fast-v3-0-2aaef02df0e1@arm.com> <20261109-refactor_gup_fast-v3-2-2aaef02df0e1@arm.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam06 X-Stat-Signature: wkjoq8dq16sghkxs6mi64878afabzpcw X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 8D1271C0006 X-Rspam-User: X-HE-Tag: 1794304336-291820 X-HE-Meta: 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 u25qGej4 sq5yQwaQS8DmlgnKhI/rbo47ja4XuFh4JNNY+EldSVkC6IVHb2cJjJiMuj7f3D8UMOOAcFpw8nQhlI4nm8rk1c3XFHOOb9HxaYAjTN3w1ftsL9pC5ou1CaVC0S7hjCDghVGBCP3fhsxxx1G+EtBxoLLJDhMRxH7WFXpCYFLc9x/AbOoO7F4vRcLtaP7X+TGLdTQKGcopA27q1qDncLWRQb8YKJ8BmRmmXORM8Zw1QTBZiaRdCtSCzDBoHENdbUQ1KkZ7Y7rBL2yB/LsboemLaVDSG4EnV3SQiTlcgFcAjnyATJfsfJuDrRy9HjKIFh4ZilGTVAvppXL3CIg5K6assbVJremtLSFo1qLbWu2PZvlP7AjiOL+Xv7MgpxWVfwcE1wbT8SIGi5hVchg+4Nc//+B9vdYj3GmKDNZuXeh3SrePk9y4= 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 Mon, Nov 09, 2026 at 10:50:32PM -0500, Rik van Riel wrote: > On Mon, 2026-11-09 at 12:32 +0000, Yeoreum Yun wrote: > > Clarify a reason to check pte/pmd in gup_fast_pte_range(). > > > > Signed-off-by: Yeoreum Yun > > --- > >  mm/gup.c | 8 ++++++++ > >  1 file changed, 8 insertions(+) > > > > diff --git a/mm/gup.c b/mm/gup.c > > index 7d43ce717b246..7f9348c633d58 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2881,6 +2881,14 @@ static unsigned long gup_fast_pte_range(pmd_t > > pmd, pmd_t *pmdp, > >   if (!folio) > >   goto pte_unmap; > >   > > + /* > > + * Recheck the PTE after grabbing the folio to > > detect concurrent > > + * unmapping or protection changes such as by KSM. > > + * > > + * Also, recheck the PMD: THP collpase can detach > > the PTE table > > collapse Okay. > > > + * while its entries remain unchaged. Checking the > > PTE alone > > unchanged Acked. > > > + * would not dtect that we are walking a detached > > page table. > > detect Sorry for typos.. > > Other than that, Reviewed-by: Rik van Riel Thanks ;) > > > + */ > >   if (unlikely(pmd_val(pmd) != > > pmd_val(pmdp_get_lockless(pmdp))) || > >       unlikely(pte_val(pte) != > > pte_val(ptep_get_lockless(ptep)))) { > >   gup_put_folio(folio, 1, flags); > > -- > All Rights Reversed. -- Sincerely, Yeoreum Yun