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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> MIME-Version: 1.0 In-Reply-To: <20250220092101.71966-1-21cnbao@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: R_RAOq5gF83yQDfyOzg8fYSMvrZyJNoZgnH2_Zzi-hU_1740094350 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: yu87g1hg6xgf6rieuzgsr6y99ry581kh X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 3DB242001A X-HE-Tag: 1740094352-963698 X-HE-Meta: U2FsdGVkX1+T+Xg2yzALNUhkHqu/8T2EzQ4hxojcmPKHeIRt7O7yJw2Ugrcnrno+pjlxVIRDzeGb71NOmCZ0W5+CXCB+oqpwE5zrLutfA+wPd3BV58xiP1RxYaehkyCOaFfc5vM0IPbuIpOB3mUEF28GqrcStoOD+o5laflKb3Zp3y4GhJ0QoGO8+3XhfF9CKjzvlaa1PpENZqbmttc/fTRq63rPewgbOeGCjYf60NUWgbJe73Y+YOqzJrta9U7Nu30oxJwAE5M3wTWuL0t9YxUImoBBeCKpE9QZ/AQk+siPobTaiLgFAX2OOojPQP3mfO4I3yXLi7WutB54wQTI70f2UsryNzMnN0W6l3IcuPDJ4v5ghW+9UV1jQG0xu+m/qVBghVAx42X+qoXQzOnolZm/O1jtPkx8UKkKdTiZW65wtlK2xJI2oN3tRehkZybsRbdVg0JRWko5RR3712t/GKWGZ5FhAsYbFAFpifr/ulz6dS8faSYA0KX9TBxhFvQEZZahgpuJa9CV2fr+ot3FUFGWtpOv06wUkhK+atb20Pgv3OmKYxFt8rkaNbExgD+/2iFDq2W8Z1rvURH9lGEwSlGeyo5PRUbl1OhznExzkKVjL+AgXe+lfJZ5BRYtiT2NIpkoJo+b1aJEkUCJJlL6HTftcdzom+FzSGNqJ4ceUp2ej/iOCpBJf0A2WNFB/cW7TNvNKzr2gkOxeju9L1UXNkzvDVoPWVMLUPC6bONQA/fcU+vvaGt8Qi718X7RKxL/WKuvmSx26F/TF+D4gCI7j8MIopqiWLqLTIimJh8b/IrQzK3X88xAoLzJbR1vdZQ29d64fyGTYzj3nYOf6LLJWH1jXjb7r6cSuYSJqIsB045/+VA0ELr83PVi2JAk35SQsMsCttTzPmMmDjuzS5eUxMP3pzs+tKXiwNVFL6Vg2mhh2+bkjrLKlIYzKE/tPoyCZmBVCZTm3GGBWm6Pev8 +HK0YUG4 vp+pbw+SpnSa3oJ96/Ijw2v9LICPU0kRH5/PT4LlMZwBHJLO74awi+Uu3KPRv4uK7tFU2UdVp5dzul+jycW3G3Ylo4pS4Jt71hiTRan9j9a0DQszYjOb9Gsx06Tz5nOl6gIloI+EDlMVkN6DkO2xV0NbBz8Re44T/KxQVhPmjumbiT1IF52AyjAPh3LmgVAC9tjO/BVW6OdGoJchCF/eo299ylaQ1zu76PpVuJinipBhpSc5kRPVEd/2lpl6IEKqif0ahIan9XsJFhN+6yCNU6BT5U+iPvrSIM9eaGKO/rkUvTqlR5KNj0cfakTSIT/TM1ae2oVmTkb9h9XSBrFoktYKudqOOuKejGBgoAosN+WCVB/ril76MbeQrzfmUQ97KSH2TTHwwudjyWGiQEs/0L4T0PNnJPV68q58u6XfCdzNtdvpYD2b4b3hKUa1PJY+qqydS X-Bogosity: Ham, tests=bogofilter, spamicity=0.139323, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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