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Howlett" , akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, surenb@google.com, kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com, david@redhat.com, axelrasmussen@google.com, bgeffon@google.com, willy@infradead.org, jannh@google.com, kaleshsingh@google.com, ngeoffray@google.com, timmurray@google.com Subject: Re: [PATCH v2 2/3] userfaultfd: protect mmap_changing with rw_sem in userfaulfd_ctx Message-ID: References: <20240129210014.troxejbr3mzorcvx@revolver> <20240130034627.4aupq27mksswisqg@revolver> <20240130172831.hv5z7a7bhh4enoye@revolver> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: s93q1ppciwah6bboaa6mykid16xbp3sk X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: ADDFA40006 X-Rspam-User: X-HE-Tag: 1707725696-994752 X-HE-Meta: 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 +jsV8ZN5 mfiIaXHHKR7HOywmt0YnbwAonSzCMWSQmxzZfv9y1FJoVjwUjkNZSWdRvwPR6yunfPURGreKtOa/xU3L1CtMvrldj0bIFnN5Y9PAelRdLyAC/phpTrfHA0HcEM0BYRKoY3xRhwKI26SIsMTFM1WFktM14vKeWyifKge9Q+EJeGieVWI1BRwNODiNVdVM9eR88a2yOK35/px47G+kCZcC+tmqAE+jbppM2gBgxeATFZrpTFh+PaSBY8RBHuHQVvvS3qDV4yP9V8Fo9561JsYC+R5ejY80YmsYFONag9Z040gWpmLODFfuhWNuEWD/+AUio0Yja 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, Feb 07, 2024 at 12:24:52PM -0800, Lokesh Gidra wrote: > On Wed, Feb 7, 2024 at 7:27 AM Mike Rapoport wrote: > > > > > > The write-lock is not a requirement here for correctness and I don't see > > > > why we would need userfaultfd_remove_prep(). > > > > > > > > As I've said earlier, having a write-lock here will let CRIU to run > > > > background copy in parallel with processing of uffd events, but I don't > > > > feel strongly about doing it. > > > > > > > Got it. Anyways, such a change needn't be part of this patch, so I'm > > > going to keep it unchanged. > > > > You mean with a read lock? > > No, I think write lock is good as it enables parallel background copy. > Also because it brings consistency in blocking userfaultfd operations. > > I meant encapsulating remove operations within > userfaultfd_remove_prep() and userfaultfd_remove_complete(). I > couldn't figure out any need for that. I don't think there is a need for that. With fork/mremap prep is required to ensure there's uffd context for new vmas. -- Sincerely yours, Mike.