tracing: Try again for saved cmdline if failed due to locking (379cfdac) · Commits · 戴 / test

In order to prevent the saved cmdline cache from being filled when tracing is not active, the comms are only recorded after a trace event is recorded. The problem is, a comm can fail to be recorded if the trace_cmdline_lock is held. That lock is taken via a trylock to allow it to happen from any context (including NMI). If the lock fails to be taken, the comm is skipped. No big deal, as we will try again later. But! Because of the code that was added to only record after an event, we may not try again later as the recording is made as a oneshot per event per CPU. Only disable the recording of the comm if the comm is actually recorded. Fixes: "tracing: Cache comms only after an event occurred" Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

+7 −6

Original line number	Diff line number	Diff line
		@@ -1441,12 +1441,12 @@ static void tracing_stop_tr(struct trace_array *tr)

		void trace_stop_cmdline_recording(void);

		static void trace_save_cmdline(struct task_struct *tsk)
		static int trace_save_cmdline(struct task_struct *tsk)
		{
		unsigned pid, idx;

		if (!tsk->pid \|\| unlikely(tsk->pid > PID_MAX_DEFAULT))
		return;
		return 0;

		/*
		* It's not the end of the world if we don't get
		@@ -1455,7 +1455,7 @@ static void trace_save_cmdline(struct task_struct *tsk)
		* so if we miss here, then better luck next time.
		*/
		if (!arch_spin_trylock(&trace_cmdline_lock))
		return;
		return 0;

		idx = map_pid_to_cmdline[tsk->pid];
		if (idx == NO_CMDLINE_MAP) {
		@@ -1480,6 +1480,8 @@ static void trace_save_cmdline(struct task_struct *tsk)
		memcpy(&saved_cmdlines[idx], tsk->comm, TASK_COMM_LEN);

		arch_spin_unlock(&trace_cmdline_lock);

		return 1;
		}

		void trace_find_cmdline(int pid, char comm[])
		@@ -1521,9 +1523,8 @@ void tracing_record_cmdline(struct task_struct *tsk)
		if (!__this_cpu_read(trace_cmdline_save))
		return;

		if (trace_save_cmdline(tsk))
		__this_cpu_write(trace_cmdline_save, false);

		trace_save_cmdline(tsk);
		}

		void

Admin message