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Mon, 12 May 2025 02:42:51 -0700 (PDT) Received: from pengdl-HP.mioffice.cn ([43.224.245.227]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-74237703f2asm5649809b3a.35.2025.05.12.02.42.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 May 2025 02:42:51 -0700 (PDT) From: pengdonglin To: rostedt@goodmis.org Cc: mhiramat@kernel.org, dolinux.peng@gmai.com, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, pengdonglin Subject: [PATCH 1/2] ftrace: Fix preemption acounting for stacktrace trigger command Date: Mon, 12 May 2025 17:42:45 +0800 Message-Id: <20250512094246.1167956-1-dolinux.peng@gmail.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: pengdonglin While using the stacktrace trigger command to trace syscalls/sys_enter_read, I noticed that the preemption count was consistently reported as 1, which seemed incorrect: root@ubuntu22-vm:/sys/kernel/tracing/events/syscalls/sys_enter_read $ echo stacktrace > trigger $ echo 1 > enable sshd-416 [002] ..... 232.864910: sys_read(fd: a, buf: 556b1f3221d0, count: 8000) sshd-416 [002] ...1. 232.864913: => ftrace_syscall_enter => syscall_trace_enter => do_syscall_64 => entry_SYSCALL_64_after_hwframe The root cause is that the trace framework disables preemption in __DO_TRACE before invoking the trigger callback. This patch uses tracing_gen_ctx_dec() to obtain the correct preemption count within the callback, resulting in accurate reporting: sshd-410 [004] ..... 210.117660: sys_read(fd: 4, buf: 559b725ba130, count: 40000) sshd-410 [004] ..... 210.117662: => ftrace_syscall_enter => syscall_trace_enter => do_syscall_64 => entry_SYSCALL_64_after_hwframe Signed-off-by: pengdonglin --- kernel/trace/trace_events_trigger.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c index b66b6d235d91..6e87ae2a1a66 100644 --- a/kernel/trace/trace_events_trigger.c +++ b/kernel/trace/trace_events_trigger.c @@ -1560,7 +1560,7 @@ stacktrace_trigger(struct event_trigger_data *data, struct trace_event_file *file = data->private_data; if (file) - __trace_stack(file->tr, tracing_gen_ctx(), STACK_SKIP); + __trace_stack(file->tr, tracing_gen_ctx_dec(), STACK_SKIP); else trace_dump_stack(STACK_SKIP); } -- 2.25.1