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Sun, 10 Nov 2024 21:51:52 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:a43c:b34:8b29:4f8]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-724079a4126sm8396292b3a.102.2024.11.10.21.51.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 10 Nov 2024 21:51:51 -0800 (PST) Date: Mon, 11 Nov 2024 14:51:46 +0900 From: Sergey Senozhatsky To: Andrii Nakryiko Cc: bpf@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, adobriyan@gmail.com, shakeel.butt@linux.dev, hannes@cmpxchg.org, ak@linux.intel.com, osandov@osandov.com, song@kernel.org, jannh@google.com, linux-fsdevel@vger.kernel.org, willy@infradead.org, Eduard Zingerman Subject: Re: [PATCH v7 bpf-next 09/10] bpf: wire up sleepable bpf_get_stack() and bpf_get_task_stack() helpers Message-ID: <20241111055146.GA1458936@google.com> References: <20240829174232.3133883-1-andrii@kernel.org> <20240829174232.3133883-10-andrii@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240829174232.3133883-10-andrii@kernel.org> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9AAB21A0006 X-Stat-Signature: isxgk3orojrgq56g1ye4fpjnkdjwpu87 X-Rspam-User: X-HE-Tag: 1731304263-810861 X-HE-Meta: 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 JTrsqpQ+ grA5/s9j9RH9GeZGrFnL2OqW8pQQFZrpRcg3yIk5DfQkEu+oRZAcOqXZggZDh5rI3R5m9i+LrNoFhJ8BJiOSeHe+2e8gyjAUNlBWOqDJKWx1+DOlPfu7sVGcqukfytZUADxdzGdafaDKg7QvOI4nT+Ir4ffV8BoWZ5rIB5b4WgYOMAHH191UVhOvrof8J+9hzaPjfLUTwpXA7a6QKF+9JBHk/gsUcUu/Az/Ym2rZee3Rgro1WXancT6glgLL34AQiQOMvlhT9y8/g+y0RaApfWshWgo6nqNiBNwkr0/TWWyQrjXR8vWbQcSqBcav/EZnwv7urIt3u+E52d92aoLY77+xxdCXSAcckFrDP8sY9TbOdRCUJoR1yg8QmhXzIbV3FXfnS9tldnFh80WBTBk6zbfpQxg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000524, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, On (24/08/29 10:42), Andrii Nakryiko wrote: > Now that build ID related internals in kernel/bpf/stackmap.c can be used > both in sleepable and non-sleepable contexts, we need to add additional > rcu_read_lock()/rcu_read_unlock() protection around fetching > perf_callchain_entry, but with the refactoring in previous commit it's > now pretty straightforward. We make sure to do rcu_read_unlock (in > sleepable mode only) right before stack_map_get_build_id_offset() call > which can sleep. By that time we don't have any more use of > perf_callchain_entry. Shouldn't this be backported to stable kernels? It seems that those still do suspicious-RCU deference: __bpf_get_stack() get_perf_callchain() perf_callchain_user() perf_get_guest_cbs()