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Thu, 07 May 2026 18:00:42 -0700 (PDT) Date: Fri, 8 May 2026 01:00:40 +0000 From: Wei Yang To: Alexander Gordeev Cc: Wei Yang , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Anshuman Khandual , Oscar Salvador , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerald Schaefer , Heiko Carstens , Vasily Gorbik Subject: Re: [PATCH v2] mm/page_vma_mapped_walk: Use ptep_get_lockless() for lockless access Message-ID: <20260508010040.o7bypjnfceeqloeq@master> Reply-To: Wei Yang References: <20260504130434.2285053-1-agordeev@linux.ibm.com> <20260507093433.q5xybwumryxclnqy@master> <43815634-29d3-4fa4-b967-0e251ff32f73-agordeev@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <43815634-29d3-4fa4-b967-0e251ff32f73-agordeev@linux.ibm.com> User-Agent: NeoMutt/20170113 (1.7.2) X-Rspam-User: X-Rspamd-Queue-Id: A56F6180004 X-Rspamd-Server: rspam04 X-Stat-Signature: k1b5sbextyiym7897wb3d997on6byexg X-HE-Tag: 1778202045-485820 X-HE-Meta: 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 /pHoMnub 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, May 07, 2026 at 12:32:09PM +0200, Alexander Gordeev wrote: >On Thu, May 07, 2026 at 09:34:33AM +0000, Wei Yang wrote: >> >@@ -310,7 +310,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >> > goto restart; >> > } >> > pvmw->pte++; >> >- } while (pte_none(ptep_get(pvmw->pte))); >> >+ } while (pte_none(ptep_get_lockless(pvmw->pte))); >> >> As Oscar mentioned in lkml.org/lkml/2026/4/27/630, map_pte() may take the >> lock. So probably it is not right? > >If I read the code correctly map_pte() might take the lock, but also >might not take it. If it took the lock and uses ptep_get_lockless(), >then it is fine. But if it did not take the lock and uses ptep_get(), >then it is an issue. > So the rule here is: * ptep_get_lockless() could be used for locked and not locked * ptep_get() only used when locked Right? >> > >> > if (!pvmw->ptl) { >> > spin_lock(ptl); >> >-- >> >2.51.0 >> > >> >> -- >> Wei Yang > >Thanks! -- Wei Yang Help you, Help me