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V" , Christoph Hellwig Subject: Re: [PATCH] mm/gup: Fix follow_devmap_p[mu]d() on page==NULL handling Message-Id: <20231124112059.3519d6fdfe71f846f8bf726f@linux-foundation.org> In-Reply-To: <20231123180222.1048297-1-peterx@redhat.com> References: <20231123180222.1048297-1-peterx@redhat.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 79CBF40026 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 7uo1ejc8fix5asdoyhizie7mmxwopj5f X-HE-Tag: 1700853662-324553 X-HE-Meta: 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 k1iRJADy /E7EaraJGNiIOEbIp1ULyOY1FDNApNgCT1kTdOf9NJlrnbGZBf+VHrhR25YaPCNQPgErlBN99RmbRJGXhtExZXlwYm3mAEBOy2Sv1yU6NQhXOT5rqSmAfNor8ndPx8gNkgUFaIYAb+nScUMFRky1gS+5ifnO6S4F67Aoo++TPUcROT3AG4qarEayd+r9bphxL7kK3UYmFFn6t0SnyNRo+dodhKjWMfG8hWElOraUNfc6FOF5e09lBRWrMX5AnEBIAFlLsuCg0X2DovW/rDeoXaDZHXPB0R6lRzXtcgZg10l6piGo= 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 Thu, 23 Nov 2023 13:02:22 -0500 Peter Xu wrote: > This is a bug found not by any report but only by code observations. > > When GUP sees a devpmd/devpud and if page==NULL is returned, it means a > fault is probably required. Here falling through when page==NULL can cause > unexpected behavior. > Well this is worrisome. We aren't able to construct a test case to demonstrate this bug? Why is that? Is it perhaps just dead code?