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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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) 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