linux-kernel - [PATCH 08/11 v2] perf/ftrace: Add recursion protection to the ftrace callback

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Message-ID: <20201030214014.321322883@goodmis.org>
Date:   Fri, 30 Oct 2020 17:31:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>, Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH 08/11 v2] perf/ftrace: Add recursion protection to the ftrace callback

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

If a ftrace callback does not supply its own recursion protection and
does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
make a helper trampoline to do so before calling the callback instead of
just calling the callback directly.

The default for ftrace_ops is going to change. It will expect that handlers
provide their own recursion protection, unless its ftrace_ops states
otherwise.

Link: https://lkml.kernel.org/r/20201028115613.444477858@goodmis.org

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_event_perf.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 643e0b19920d..fd58d83861d8 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -439,10 +439,15 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
 	struct hlist_head head;
 	struct pt_regs regs;
 	int rctx;
+	int bit;
 
 	if ((unsigned long)ops->private != smp_processor_id())
 		return;
 
+	bit = ftrace_test_recursion_trylock();
+	if (bit < 0)
+		return;
+
 	event = container_of(ops, struct perf_event, ftrace_ops);
 
 	/*
@@ -463,13 +468,15 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
 
 	entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
 	if (!entry)
-		return;
+		goto out;
 
 	entry->ip = ip;
 	entry->parent_ip = parent_ip;
 	perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
 			      1, &regs, &head, NULL);
 
+out:
+	ftrace_test_recursion_unlock(bit);
 #undef ENTRY_SIZE
 }
 
-- 
2.28.0