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Thu, 20 Feb 2025 15:32:29 -0800 (PST) X-Google-Smtp-Source: AGHT+IGFRu2Dnc+2Q7aLVvcud0WLNtdkmcDWf2h64KzsKzPXi5Ef2jfC4H9CsgJUUAwL7iouzkB4kA== X-Received: by 2002:a05:620a:4512:b0:7c0:a272:65a7 with SMTP id af79cd13be357-7c0cf0e2eaamr178560085a.2.1740094349435; Thu, 20 Feb 2025 15:32:29 -0800 (PST) Received: from x1.local ([2604:7a40:2041:2b00::1000]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c09d8d4fb4sm542978785a.55.2025.02.20.15.32.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2025 15:32:28 -0800 (PST) Date: Thu, 20 Feb 2025 18:32:25 -0500 From: Peter Xu To: Barry Song <21cnbao@gmail.com> Cc: david@redhat.com, Liam.Howlett@oracle.com, aarcange@redhat.com, akpm@linux-foundation.org, axelrasmussen@google.com, bgeffon@google.com, brauner@kernel.org, hughd@google.com, jannh@google.com, kaleshsingh@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lokeshgidra@google.com, mhocko@suse.com, ngeoffray@google.com, rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, v-songbaohua@oppo.com, viro@zeniv.linux.org.uk, willy@infradead.org, zhangpeng362@huawei.com, zhengtangquan@oppo.com, yuzhao@google.com, stable@vger.kernel.org Subject: Re: [PATCH RFC] mm: Fix kernel BUG when userfaultfd_move encounters swapcache Message-ID: References: <69dbca2b-cf67-4fd8-ba22-7e6211b3e7c4@redhat.com> <20250220092101.71966-1-21cnbao@gmail.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250220092101.71966-1-21cnbao@gmail.com> On Thu, Feb 20, 2025 at 10:21:01PM +1300, Barry Song wrote: > 2. src_anon_vma and its lock – swapcache doesn’t require it（folio is not mapped） Could you help explain what guarantees the rmap walk not happen on a swapcache page? I'm not familiar with this path, though at least I see damon can start a rmap walk on PageAnon almost with no locking.. some explanations would be appreciated. -- Peter Xu