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Thu, 07 May 2026 23:23:39 -0700 (PDT) Date: Fri, 8 May 2026 06:23:38 +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: <20260508062338.h7xmz3hjzozdrg5t@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> <20260508010040.o7bypjnfceeqloeq@master> <4da2d354-808d-463e-ac85-5b1f3fd51618-agordeev@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4da2d354-808d-463e-ac85-5b1f3fd51618-agordeev@linux.ibm.com> User-Agent: NeoMutt/20170113 (1.7.2) X-Stat-Signature: poswc6e3x3pam51hi7fn1poapgytqguj X-Rspamd-Queue-Id: 893C4C0012 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1778221422-861947 X-HE-Meta: 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 fo3ACBaH 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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 Fri, May 08, 2026 at 07:15:45AM +0200, Alexander Gordeev wrote: >On Fri, May 08, 2026 at 01:00:40AM +0000, Wei Yang wrote: >> 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? > >Yes, this is my assumption. > Thanks, if so, it looks good. >> >> > >> >> > if (!pvmw->ptl) { >> >> > spin_lock(ptl); >> >> >-- >> >> >2.51.0 >> >> > >> >> >> >> -- >> >> Wei Yang >> > >> >Thanks! >> >> -- >> Wei Yang >> Help you, Help me -- Wei Yang Help you, Help me