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Tue, 02 Jan 2024 01:00:15 -0800 (PST) X-Google-Smtp-Source: AGHT+IHrXpLdU+hn5Ohkn+pL4MWX99S7hACEAUpLWxDWVhqo29Z1a8GD0ci/X/NzUkbZnrDM1DPA+g== X-Received: by 2002:a17:90a:bd17:b0:28c:113a:9678 with SMTP id y23-20020a17090abd1700b0028c113a9678mr23773618pjr.4.1704186013844; Tue, 02 Jan 2024 01:00:13 -0800 (PST) Received: from x1n ([43.228.180.230]) by smtp.gmail.com with ESMTPSA id w5-20020a17090a6b8500b0028bd0a43bc9sm24391031pjj.2.2024.01.02.01.00.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jan 2024 01:00:13 -0800 (PST) Date: Tue, 2 Jan 2024 16:59:56 +0800 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, david@redhat.com, ryan.roberts@arm.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 1/1] userfaultfd: fix move_pages_pte() splitting folio under RCU read lock Message-ID: References: <20231230025607.2476912-1-surenb@google.com> MIME-Version: 1.0 In-Reply-To: <20231230025607.2476912-1-surenb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 1C5E6C000A X-Stat-Signature: dhha6q7fwk85ucmopgb3mtdkdxxjpous X-Rspam-User: X-HE-Tag: 1704186017-233853 X-HE-Meta: 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 EBScEla3 /PnEz0QqWXxhdnMr0XlxOILmmmprWgmmDn1JejRNEmTMKBYY5X6JthOo8azAW7Z2HDMq04eF/3iOtaGLN513haHYmyhoEaIzU0PSR0BSX5Yc0dNuRRoKx/8brV49os6t8rHYu5WT8d/c+fwkiHruLGy8hkDjIMswIhu3mxABOtalCmzpIJM7MxhI52wzzcVurF+jGTtamV5L6d/vQ8ymt9PviVn1OtTS0+w6fGc6/mpH445ipGUbfzurjvaQ7fz7ppyZBP/oc3vZbkLlHeaAtKFCSfQFJsbyRyMBIVUuAX6KAGR7OK5AvEL1mVZu1/LO/yllwjkH6bw8zyaXE+GBZO41QcWEtXySOmCcd4ISMIso0JqowzM6TCga2ER0WP9z8GBJ61gSGISTSSTug6avw48XFj7NJMhYW3mmxa6kAFOtWej5qKdPVfULszA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Fri, Dec 29, 2023 at 06:56:07PM -0800, Suren Baghdasaryan wrote: > @@ -1078,9 +1078,14 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > > /* at this point we have src_folio locked */ > if (folio_test_large(src_folio)) { > + /* split_folio() can block */ > + pte_unmap(&orig_src_pte); > + pte_unmap(&orig_dst_pte); > + src_pte = dst_pte = NULL; > err = split_folio(src_folio); > if (err) > goto out; > + goto retry; > } Do we also need to clear src_folio and src_folio_pte? If the folio is a thp, I think it means it's pte mapped here. Then after the split we may want to fetch the small folio after the split, not the head one? -- Peter Xu