linux-kernel - [PATCH] tracing: ignore FTRACE_FL_DISABLED while walking dyn

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Message-ID: <1478560460-3818619-1-git-send-email-ast@fb.com>
Date:   Mon, 7 Nov 2016 15:14:20 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Dave Jones <davej@...emonkey.org.uk>,
        Martin KaFai Lau <kafai@...com>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...com>
Subject: [PATCH] tracing: ignore FTRACE_FL_DISABLED while walking dyn_ftrace records

ftrace_shutdown() checks for sanity of ftrace records
and if dyn_ftrace->flags is not zero, it will warn.
It can happen that 'flags' are set to FTRACE_FL_DISABLED at this point,
since some module was loaded, but before ftrace_module_enable()
cleared the flags for this module.

In other words the module.c is doing:
ftrace_module_init(mod); // calls ftrace_update_code() that sets flags=FTRACE_FL_DISABLED
... // here ftrace_shutdown() is called that warns, since
err = prepare_coming_module(mod); // didn't have a chance to clear FTRACE_FL_DISABLED

Fix it by ignoring disabled records.
It's similar to what __ftrace_hash_rec_update() is already doing.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
---
 kernel/trace/ftrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2050a7652a86..326498baab83 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2763,7 +2763,7 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
 		struct dyn_ftrace *rec;

 		do_for_each_ftrace_rec(pg, rec) {
-			if (FTRACE_WARN_ON_ONCE(rec->flags))
+			if (FTRACE_WARN_ON_ONCE(rec->flags & ~FTRACE_FL_DISABLED))
 				pr_warn("  %pS flags:%lx\n",
 					(void *)rec->ip, rec->flags);
 		} while_for_each_ftrace_rec();
-- 
2.8.0