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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jiri Olsa <jolsa@redhat.com>
Subject: [PATCH 8/9] perf/ftrace: Check for rcu_is_watching() in callback function
Date: Wed, 28 Oct 2020 07:52:52 -0400	[thread overview]
Message-ID: <20201028115613.591878956@goodmis.org> (raw)
In-Reply-To: 20201028115244.995788961@goodmis.org

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a ftrace callback requires "rcu_is_watching", then it adds the
FTRACE_OPS_FL_RCU flag and it will not be called if RCU is not "watching".
But this means that it will use a trampoline when called, and this slows
down the function tracing a tad. By checking rcu_is_watching() from within
the callback, it no longer needs the RCU flag set in the ftrace_ops and it
can be safely called directly.

Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_event_perf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index fd58d83861d8..a2b9fddb8148 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -441,6 +441,9 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
 	int rctx;
 	int bit;
 
+	if (!rcu_is_watching())
+		return;
+
 	if ((unsigned long)ops->private != smp_processor_id())
 		return;
 
@@ -484,7 +487,6 @@ static int perf_ftrace_function_register(struct perf_event *event)
 {
 	struct ftrace_ops *ops = &event->ftrace_ops;
 
-	ops->flags   = FTRACE_OPS_FL_RCU;
 	ops->func    = perf_ftrace_function_call;
 	ops->private = (void *)(unsigned long)nr_cpu_ids;
 
-- 
2.28.0



  parent reply	other threads:[~2020-10-28 22:17 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-28 11:52 [PATCH 0/9] ftrace: Have callbacks handle their own recursion Steven Rostedt
2020-10-28 11:52 ` [PATCH 1/9] ftrace: Move the recursion testing into global headers Steven Rostedt
2020-10-30  9:13   ` Miroslav Benes
2020-10-30 12:30     ` Steven Rostedt
2020-10-28 11:52 ` [PATCH 2/9] ftrace: Add ftrace_test_recursion_trylock() helper function Steven Rostedt
2020-10-28 11:52 ` [PATCH 3/9] ftrace: Optimize testing what context current is in Steven Rostedt
2020-10-28 11:52 ` [PATCH 4/9] pstore/ftrace: Add recursion protection to the ftrace callback Steven Rostedt
2020-10-28 15:59   ` Kees Cook
2020-10-28 11:52 ` [PATCH 5/9] kprobes/ftrace: " Steven Rostedt
2020-10-28 11:52   ` Steven Rostedt
2020-10-29  7:58   ` Masami Hiramatsu
2020-10-29  7:58     ` Masami Hiramatsu
2020-10-29 13:40     ` Steven Rostedt
2020-10-29 13:40       ` Steven Rostedt
2020-11-02  5:08       ` Masami Hiramatsu
2020-11-02  5:08         ` Masami Hiramatsu
2020-10-28 11:52 ` [PATCH 6/9] livepatch/ftrace: " Steven Rostedt
2020-10-29 13:51   ` Miroslav Benes
2020-10-29 14:37     ` Steven Rostedt
2020-10-30 12:28       ` Steven Rostedt
2020-10-29 14:57     ` Petr Mladek
2020-10-29 15:03       ` Miroslav Benes
2020-10-29 18:24       ` Steven Rostedt
2020-10-30  9:48         ` Miroslav Benes
2020-10-30 10:41           ` Petr Mladek
2020-10-28 11:52 ` [PATCH 7/9] perf/ftrace: " Steven Rostedt
2020-10-28 11:52 ` Steven Rostedt [this message]
2020-10-28 11:52 ` [PATCH 9/9] ftrace: Reverse what the RECURSION flag means in the ftrace_ops Steven Rostedt

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