[for-next][PATCH] tracing: Fix incorrect enabling of trace events by boot cmdline

[Steven Rostedt]

Another small fix that I'll push in this merge window.

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
for-next

Head SHA1: 84fce9db4d7eaebd6cb2ee30c15da6d4e4daf846


Joonsoo Kim (1):
      tracing: Fix incorrect enabling of trace events by boot cmdline

----
 kernel/trace/trace_events.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---------------------------
commit 84fce9db4d7eaebd6cb2ee30c15da6d4e4daf846
Author: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Date:   Thu Apr 16 13:44:44 2015 +0900

    tracing: Fix incorrect enabling of trace events by boot cmdline
    
    There is a problem that trace events are not properly enabled with
    boot cmdline. The problem is that if we pass "trace_event=kmem:mm_page_alloc"
    to the boot cmdline, it enables all kmem trace events, and not just
    the page_alloc event.
    
    This is caused by the parsing mechanism. When we parse the cmdline, the buffer
    contents is modified due to tokenization. And, if we use this buffer
    again, we will get the wrong result.
    
    Unfortunately, this buffer is be accessed three times to set trace events
    properly at boot time. So, we need to handle this situation.
    
    There is already code handling ",", but we need another for ":".
    This patch adds it.
    
    Link: http://lkml.kernel.org/r/1429159484-22977-1-git-send-email-iamjoonsoo.kim@xxxxxxx
    
    Cc: stable@xxxxxxxxxxxxxxx # 3.19+
    Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
    [ added missing return ret; ]
    Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index a576bbe75577..36a957c996c7 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -565,6 +565,7 @@ static int __ftrace_set_clr_event(struct trace_array *tr, const char *match,
 static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
 {
 	char *event = NULL, *sub = NULL, *match;
+	int ret;
 
 	/*
 	 * The buf format can be <subsystem>:<event-name>
@@ -590,7 +591,13 @@ static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
 			event = NULL;
 	}
 
-	return __ftrace_set_clr_event(tr, match, sub, event, set);
+	ret = __ftrace_set_clr_event(tr, match, sub, event, set);
+
+	/* Put back the colon to allow this to be called again */
+	if (buf)
+		*(buf - 1) = ':';
+
+	return ret;
 }
 
 /**
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