[PATCH 4.9 009/144] tracing: Quiet gcc warning about maybe unused link variable

From: Greg Kroah-Hartman
Date: Wed Aug 01 2018 - 13:25:31 EST

4.9-stable review patch. If anyone has any objections, please let me know.


From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

commit 2519c1bbe38d7acacc9aacba303ca6f97482ed53 upstream.

Commit 57ea2a34adf4 ("tracing/kprobes: Fix trace_probe flags on
enable_trace_kprobe() failure") added an if statement that depends on another
if statement that gcc doesn't see will initialize the "link" variable and
gives the warning:

"warning: 'link' may be used uninitialized in this function"

It is really a false positive, but to quiet the warning, and also to make
sure that it never actually is used uninitialized, initialize the "link"
variable to NULL and add an if (!WARN_ON_ONCE(!link)) where the compiler
thinks it could be used uninitialized.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 57ea2a34adf4 ("tracing/kprobes: Fix trace_probe flags on enable_trace_kprobe() failure")
Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

kernel/trace/trace_kprobe.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -359,7 +359,7 @@ static struct trace_kprobe *find_trace_k
static int
enable_trace_kprobe(struct trace_kprobe *tk, struct trace_event_file *file)
- struct event_file_link *link;
+ struct event_file_link *link = NULL;
int ret = 0;

if (file) {
@@ -385,7 +385,9 @@ enable_trace_kprobe(struct trace_kprobe

if (ret) {
if (file) {
- list_del_rcu(&link->list);
+ /* Notice the if is true on not WARN() */
+ if (!WARN_ON_ONCE(!link))
+ list_del_rcu(&link->list);
tk->tp.flags &= ~TP_FLAG_TRACE;
} else {