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Shutemov" , Lorenzo Stoakes , Axel Rasmussen , Matthew Wilcox , John Hubbard , Mike Rapoport , Hugh Dickins , David Hildenbrand , Andrea Arcangeli , Rik van Riel , James Houghton , Yang Shi , Jason Gunthorpe , Vlastimil Babka , Andrew Morton Subject: Re: [PATCH RFC 05/12] mm/gup: Fix follow_devmap_p[mu]d() to return even if NULL Message-ID: References: <20231116012908.392077-1-peterx@redhat.com> <20231116012908.392077-6-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231116012908.392077-6-peterx@redhat.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: CAF1640005 X-Rspam-User: X-Stat-Signature: 5pd8i8humwcme35315nik4krwic7a6gw X-Rspamd-Server: rspam03 X-HE-Tag: 1700724331-814099 X-HE-Meta: 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 8w2B64qK e6It/mHbvCAnD5cuBkmcei3ggwdaXCbdK6FMGyXseLeaGsU3FRvUC01ziP9V7LPoc9IO032QqaeGhUfgn/3WtEjE7evsdzlUqz+TDuxZNXPHFj9S9g2wolxqOSWiEzMQb+gvaVzCHF3P6DUAmThG8jB7/lBtPl06J8IiZsFb+rd0qY+ZIv5C+zsYOOvsBV3rFiQyryJRUr8nJ9qyMQXqfsy6n9WuIkoZYV49nzDzJ1vDhlSN452bMKDzqW19I9KsZJzECeQZrmClhonPpUs1mZLTfO6n/Q7DjIDwy8MncT+us6sI1pwLL+h4Pefd+kZTyF8wVN+WHmouUR34MWOaNz7zpyAYRx5apaZJlFXgEcfv58yjJ2rrtyHcQ8H/h62q9Rgn1dNkfvZ+UCDqtEjgzbSIYX5FXVYHmdo9ZYNyc8nFTlICCEkY4a9WFT+i/g8TQ0eqdhr3R7dxO9Po= 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 Wed, Nov 15, 2023 at 08:29:01PM -0500, Peter Xu wrote: > This seems to be a bug not by any report but by code observations. > > When GUP sees a devpmd or devpud, it should return whatever value returned > from follow_devmap_p[mu]d(). If page==NULL returned, it means a fault is > probably required. Skipping return the NULL should allow the code to fall > through, which can cause unexpected behavior. > > It was there at least before the follow page rework (080dbb618b) in 2017, > so 6 years. Not yet digging for a Fixes, assuming it can hardly trigger > even if the logical bug does exist. > > Signed-off-by: Peter Xu I'd still add a fixes tag and send if off to Linux for 6.7-rc instead of letting it linger. Otherwise looks good: Reviewed-by: Christoph Hellwig