tracing: Quiet gcc warning about maybe unused link variable

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@vger.kernel.org
Fixes: 57ea2a34adf4 ("tracing/kprobes: Fix trace_probe flags on enable_trace_kprobe() failure")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 27ace4513c43ba965f6ff0c1e7525c5daca0b47e..6b71860f3998c8df990b7e089075a56f759c4306 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -400,7 +400,7 @@ static struct trace_kprobe *find_trace_kprobe(const char *event,
 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) {
@@ -426,7 +426,9 @@ enable_trace_kprobe(struct trace_kprobe *tk, struct trace_event_file *file)
 
        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);
                        kfree(link);
                        tk->tp.flags &= ~TP_FLAG_TRACE;
                } else {