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Wed, 16 Oct 2024 02:57:25 -0700 (PDT) MIME-Version: 1.0 References: <20241014182228.1941246-1-joannelkoong@gmail.com> <20241014182228.1941246-3-joannelkoong@gmail.com> <8eec0912-7a6c-4387-b9be-6718f438a111@linux.alibaba.com> In-Reply-To: <8eec0912-7a6c-4387-b9be-6718f438a111@linux.alibaba.com> From: Miklos Szeredi Date: Wed, 16 Oct 2024 11:57:13 +0200 Message-ID: Subject: Re: [PATCH v2 2/2] fuse: remove tmp folio for writebacks and internal rb tree To: Jingbo Xu Cc: Shakeel Butt , Joanne Koong , linux-fsdevel@vger.kernel.org, josef@toxicpanda.com, bernd.schubert@fastmail.fm, hannes@cmpxchg.org, linux-mm@kvack.org, kernel-team@meta.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Stat-Signature: 7a8kecc6gj54qkmt6ezxwusxy184mtu9 X-Rspamd-Queue-Id: ADA591C001E X-Rspamd-Server: rspam11 X-HE-Tag: 1729072630-32613 X-HE-Meta: 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 v0TicIh6 h9R+4lmtdOAH98u4wu8cSv9K2ayaZD2BQDrPLZty5tsDKQx3yJeBWyCQulhGROmZgiEY8/0Kk2FZ7ZAMPhOzIiGCv4kkuuEzcZjNeW7iidNgZNZhQQ5JKqMWVZd1SzjCHd0xDDVugbjAuFdAJm/c+O0QmTrmfYHTHDrnvUcWENiLTFw7roNGomjPVo3crrfBmrQ7+xE4BxYShnhLZOjYR8uo8+Beg/0eNTq/P X-Bogosity: Ham, tests=bogofilter, spamicity=0.081707, 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, 16 Oct 2024 at 11:44, Jingbo Xu wrote: > 1) a non-malicious fuse daemon wants to allocate some memory when > processing a fuse request, which in turn leads to memory reclaim and > thus waiting on the writeback of fuse dirty pages - a deadlock here. > This is reasonable and also the target scenario that this series wants > to fix. > > 2) a malicious fuse daemon refuses to process any request; or a buggy or > not well-written fuse daemon as you described, e.g. may call sync(2) > itself or access page cache backed by itself, then > 2.1) any unrelated user process attempting to initiate a sync(2) > itself, will hang there. This scenario is also unexpected and shall be > fixed. Exactly. We only care about - properly written server not deadlocking - buggy or malicious server not denying service to unrelated tasks, where unrelated means it would not otherwise be able to access the fuse mount. Typically this separation is done with a user namespace or -oallow_other. Thanks, Miklos > 2.2) any direct user of fuse filesystem (e.g. access files backed by > fuse filesystem) will hang in this case. IMHO this is expected, and the > impact is affordable as it is controlled within certain range (the > direct user of the fs). > > -- > Thanks, > Jingbo