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Date: Tue, 28 Mar 2017 22:58:43 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Namhyung Kim <namhyung@...nel.org> Cc: Ingo Molnar <mingo@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, LKML <linux-kernel@...r.kernel.org>, kernel-team@....com Subject: Re: [PATCH 1/4] ftrace: Fix function pid filter on instances On Wed, 29 Mar 2017 11:42:27 +0900 Namhyung Kim <namhyung@...nel.org> wrote: > On Tue, Mar 28, 2017 at 10:28:55PM -0400, Steven Rostedt wrote: > > On Wed, 29 Mar 2017 11:20:37 +0900 > > Namhyung Kim <namhyung@...nel.org> wrote: > > > > > > > > Actually, if this is called after event_trace_del_tracer(), the tr is > > > > already invisible and nothing new should change. > > > > > > I don't follow. After event_trace_del_tracer(), the tr is invisible > > > from the probe of event tracing but still is visible from the probe of > > > function tracing, right? > > > > Well, nothing should be able to get to the set_ftrace_filter file when > > there. Because of the tr->ref count. But keeping the lock is safer > > regardless, and it's not a fast path, so the extra overhead if the lock > > isn't needed is no big deal. > > Oh, I meant if a pid filter was already set when removing the > instance. Function filters should be inactive since function tracer > was finished (via tracing_set_nop), but the probe on sched_switch > event (for pid filter) is still active and references the tr. > I think we are talking about two different things. I was simply talking about the need to take the ftrace_lock or not in the clear_ftrace_pids() call here. I don't think we have to, because nothing should be in contention with it at that point. But it doesn't hurt to take it. -- Steve
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