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Thu, 26 Dec 2024 17:02:02 -0500 (EST) Message-ID: Date: Thu, 26 Dec 2024 23:02:01 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings To: Shakeel Butt , David Hildenbrand Cc: Joanne Koong , Zi Yan , miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko References: <2bph7jx4hvhxpgp77shq2j7mo4xssobhqndw5v7hdvbn43jo2w@scqly5zby7bm> <71d7ac34-a5e5-4e59-802b-33d8a4256040@redhat.com> <9404aaa2-4fc2-4b8b-8f95-5604c54c162a@redhat.com> <3f3c7254-7171-4987-bb1b-24c323e22a0f@redhat.com> From: Bernd Schubert Content-Language: en-US, de-DE, fr In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DE08518000E X-Stat-Signature: c6dp6b83a5943wyxfibptqd58ysd69dm X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1735250496-884136 X-HE-Meta: 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 KDychNDe +6huW1yCu7Rhd5x5aFT+tni8/sYEWNyYJyl5KLpeSNIYexNPKZf7nbtQKrKmBPln7H+7H+KB5vQOcRKnsL7wj+8dX3dlPyJZIRo0vuSJ2mHKsGN+dVNIeBzRJ3mMlTASXRmPJsPcO0jpWtji1XPZ/7887lSIeZYpeHaAoaABq1q4/Lw1pYXu/+nPVYnCg2+nN8Gy+WorXe91zzbThGV2KpTyQmymKLEQOIVa3BJBMAQ1B93m0og8BcJt0EvUffu3BgV3T0MNBkW0BDGgvTMpgOQC9qKoWMgiKiKYGqr0jp+ZaTPNZT/d1nejVOJ/sETyNnWhc6ZQFx/E0n6KStydD7KxwNP1ba03ff0HuDsxYyc8PapB4Nh2ZQj9MLgrDauko3MVb9yqh/ZaiNn7JGUfa/mdOSg== 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 12/26/24 21:13, Shakeel Butt wrote: > On Tue, Dec 24, 2024 at 01:37:49PM +0100, David Hildenbrand wrote: >> On 23.12.24 23:14, Shakeel Butt wrote: >>> On Sat, Dec 21, 2024 at 05:18:20PM +0100, David Hildenbrand wrote: >>>> >>> >>> I think you have valid concerns but these are not new and not unique to >>> fuse. Any filesystem with a potential arbitrary stall can have similar >>> issues. The arbitrary stall can be caused due to network issues or some >>> faultly local storage. >> >> What concerns me more is that this is can be triggered by even unprivileged >> user space, and that there is no default protection as far as I understood, >> because timeouts cannot be set universally to a sane defaults. >> >> Again, please correct me if I got that wrong. >> > > Let's route this question to FUSE folks. More specifically: can an > unprivileged process create a mount point backed by itself, create a > lot of dirty (bound by cgroup) and writeback pages on it and let the > writeback pages in that state forever? libfuse provides 'fusermount' which has the s-bit set. I think most distributions take that over into their libfuse packages. The fuse-server process then continues to run as arbitrary user.