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Fri, 06 Nov 2026 21:40:12 -0800 (PST) Received: from lipengfei28-ThinkStation-P368.mioffice.cn ([2408:8607:1b00:8:a1a:7bc2:20ba:a479]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ed47da11afsm10992515ad.72.2026.11.06.21.40.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 21:40:11 -0800 (PST) From: Li Pengfei X-Google-Original-From: Li Pengfei To: rostedt@goodmis.org, mhiramat@kernel.org Cc: mathieu.desnoyers@efficios.com, mark.rutland@arm.com, corbet@lwn.net, skhan@linuxfoundation.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, zhangbo56@xiaomi.com, lipengfei28@xiaomi.com Subject: Re: [RFC PATCH v7 01/10] trace: add lock-free stackmap for stack trace deduplication Date: Sat, 7 Nov 2026 13:39:54 +0800 Message-Id: <20261107053954.3075147-1-lipengfei28@xiaomi.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20261103174905.701e078a@gandalf.local.home> References: <20260912083753.3426176-1-lipengfei28@xiaomi.com> <20260912083753.3426176-2-lipengfei28@xiaomi.com> <20261103174905.701e078a@gandalf.local.home> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Pengfei Li On Tue, 3 Nov 2026 17:49:05 -0500 Steven Rostedt wrote: > Let's get rid of using rcu_tasks_rude. If RCU isn't watching, then we > simply discard the stack trace. We do not want to add any more code that > relies on it. If an architecture wants this feature, then it needs to > update to not allow tracing without RCU watching. OK. v8 checks rcu_is_watching() before it loads the map and only uses synchronize_rcu() for reset and free. When RCU is not watching, the stack is discarded. > There's no reason to use a rw semaphore here. Just use a mutex. It's > serializing the reads of the stackmaps from user space right? There's no > reason to have more than one reader at a time. Yes. v8 uses a mutex. > Instead of duplicating the open coded free in ftrace_stackmap_create(), > move this ftrace_stackmap_destroy() above that function and call it on fail. Done in v8. > The above paragraph is unnecessary here. If you want to add it to kernel > docs where it is user visible, then fine. (I haven't looked yet if you > already did). The docs cover it, so the paragraph goes. Thanks, Pengfei Li