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Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1pLDQk-004M0M-30; Fri, 27 Jan 2023 01:21:27 +0000 Date: Fri, 27 Jan 2023 01:21:26 +0000 From: Al Viro To: David Howells Cc: David Hildenbrand , Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Jason Gunthorpe , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christoph Hellwig , John Hubbard Subject: Re: [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator Message-ID: References: <20230126141626.2809643-1-dhowells@redhat.com> <20230126141626.2809643-3-dhowells@redhat.com> <2907150.1674777410@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: BAADB80015 X-Rspamd-Server: rspam01 X-Stat-Signature: zbz3diajpuxorjgtm8yb4pxp4dz1c8gu X-HE-Tag: 1674782500-897233 X-HE-Meta: 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 ObLnSmmS TBFP2laMw/pZxf33feANF22P0C7ucLpLTCmV2RNdSgKtzHSl45E9Cj/VTml5DDXpyFR26ymTilP98u3IHe8IhTr+a3b9HABNJ+XKe8Teoxauq4mqJiKCXa/dSCp7yR4Ht1OQh9xHsw0YWM2Km5zKLn8DH9PKUZhK8m8Wbc+zUCLy+R2Dp2F/IThLqDZ1L3sjGCpRW7cSIgU3K4qvAJ5kwX+bNthmLfymK8CuRHXbLbsx3DPsGPBKazA0CUq8SHgQnsOlXtcbCFZ9JJgApHHh4Z0UgHkxkGaLcXZdBICWb8m2DtQA8cxx7Y74lhxfWcwTK2ChgUGksAQY1kQb5YMYyU96oIFLDlxTck2TophsqVNtari3LuchgRDJU9XCRBUbxtZZJqZqdSJWhQtz5l70cR/rWH7/sXMzWk89ubVu3BSpAmMfx9LVzPq4aP3icFknXJ7Y36eAGWQxZKfdtg+NXC0gQDUdy5wl4UNcy 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: On Fri, Jan 27, 2023 at 12:52:38AM +0000, Al Viro wrote: > On Thu, Jan 26, 2023 at 11:56:50PM +0000, David Howells wrote: > > Al says that pinning a page (ie. FOLL_PIN) could cause a deadlock if a page is > > vmspliced into a pipe with the pipe holding a pin on it because pinned pages > > are removed from all page tables. Is this actually the case? I can't see > > offhand where in mm/gup.c it does this. > > It doesn't; sorry, really confused memories of what's going on, took a while > to sort them out (FWIW, writeback is where we unmap and check if page is > pinned, while pin_user_pages running into an unmapped page will end up > with handle_mm_fault() (->fault(), actually) try to get the sucker locked > and block on that until the writeback is over). Umm... OK, I really need to reread that area. Hopefully will be done with that by tomorrow...