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AJvYcCWD+72PkTcLyGJh3OZ8YWaeBofUOZtq31EH3p2jI5hn4MstKQ4LIH+0bG4KaidQNdbNGNmrtA+8iw==@kvack.org X-Gm-Message-State: AOJu0YyEdoIyCo1HYSkdN19QNf8z5y1EYyzNdJCiTvfWZnwRJb5N+Vgj qPzc1F7D2A1WlwJUmofaSOpEzmnrr/MFKurr4TZbj6jFFBUHXxzX6Ce6trQ3SxaGKKTLsS3N47q gXzmsqqLmGcwZeGSHtvDU+n9fRvA= X-Google-Smtp-Source: AGHT+IEWzIrSjrNtEvKMO440O7fdoRp62ef79uEnejMaUjsk0dIVB65DxKQYHNe6tCIKxr+tm1ziHTzX0Fh2nUC80Bw= X-Received: by 2002:a17:90b:889:b0:2d8:77cc:85e with SMTP id 98e67ed59e1d1-2e1e6391a8bmr5375612a91.37.1728071892548; Fri, 04 Oct 2024 12:58:12 -0700 (PDT) MIME-Version: 1.0 References: <20241001225207.2215639-1-andrii@kernel.org> <20241001225207.2215639-4-andrii@kernel.org> <20241003-lachs-handel-4f3a9f31403d@brauner> <20241004-holzweg-wahrgemacht-c1429b882127@brauner> In-Reply-To: <20241004-holzweg-wahrgemacht-c1429b882127@brauner> From: Andrii Nakryiko Date: Fri, 4 Oct 2024 12:58:00 -0700 Message-ID: Subject: Re: [PATCH v2 tip/perf/core 3/5] fs: add back RCU-delayed freeing of FMODE_BACKING file To: Christian Brauner Cc: Andrii Nakryiko , linux-trace-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, mjguzik@gmail.com, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, mingo@kernel.org, Amir Goldstein Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: EAB5F40012 X-Stat-Signature: 46ctsajd8mntstei93w4wdk8jqd86opd X-Rspam-User: X-HE-Tag: 1728071896-34496 X-HE-Meta: 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 zbxgReIV vGeICLIVA1EwOX4S5MgwFKMlQQHDYDpiKc6qKXOWJuhKecBPde69pMx0gvK2u7Vrv3J3Axj6JoaxPYiG3KlQDoSTs36aDLGKMDDEH+MymIaGLgKDXA6heQPMQ+ImRYqE5j4Sw1pkpbclhDk74AJ/uT5Iajal80t7FKC/4mD31/gImiEX022dqUnkYLew8xxOaKBQTe0xlg5Q8QVYuJzZCCUvkWBLj1RXCczaA09cK4rlEhscw/4l71EIMqm91oNLAGGRTUC07ZCkVfjridfdqzeMKthp9K2HbkD3+tfPezt80yJcQjK1wSoFMTrmSErT3tdgzWzyuruQRwMb3emaJoRY6KtpxEw+5LV3PoCyKaMLyKzK8qx1aFNSu7mzgphF/bf0fh/Fc6R4/TB0iYe2YT/R5ZlCjYFh/eiutPFqjNnbhMTUgRVrcWy4SdtsTZvu03z+XSdFSb9eYSwahD6eeWsz4IA== 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 Fri, Oct 4, 2024 at 1:01=E2=80=AFAM Christian Brauner wrote: > > On Thu, Oct 03, 2024 at 11:13:54AM GMT, Christian Brauner wrote: > > On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote: > > > 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING > > > files to direct freeing as back then there were no use cases requirin= g > > > RCU protected access to such files. > > > > > > Now, with speculative lockless VMA-to-uprobe lookup logic, we do need= to > > > have a guarantee that struct file memory is not going to be freed fro= m > > > under us during speculative check. So add back RCU-delayed freeing > > > logic. > > > > > > We use headless kfree_rcu_mightsleep() variant, as file_free() is onl= y > > > called for FMODE_BACKING files in might_sleep() context. > > > > > > Suggested-by: Suren Baghdasaryan > > > Cc: Christian Brauner > > > Cc: Amir Goldstein > > > Signed-off-by: Andrii Nakryiko > > > --- > > > > Reviewed-by: Christian Brauner > > Fwiw, I have another patch series for files that I'm testing that will > require me to switch FMODE_BACKING to a SLAB_TYPSAFE_BY_RCU cache. That > shouldn't matter for your use-case though. Correct, we assume SLAB_TYPESAFE_BY_RCU semantics for the common case anyways. But hopefully my change won't cause major merge conflicts with your patch set.