fprobe: add unlock to match a succeeded ftrace_test_recursion_trylock

Unlock ftrace recursion lock when fprobe_kprobe_handler() is failed
because of some running kprobe.

Link: https://lore.kernel.org/all/[e-mail]/

Fixes: 3cc4e2c5fbae ("fprobe: make fprobe_kprobe_handler recursion free")
Reported-by: Yafang <[e-mail]>
Closes: https://lore.kernel.org/linux-trace-kernel/CALOAHbC6UpfFOOibdDiC7xFc5YFUgZnk3MZ=3Ny6we=[e-mail]/
Signed-off-by: Ze Gao <[e-mail]>
Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Acked-by: Yafang Shao <[e-mail]>
Reviewed-by: Steven Rostedt (Google) <[e-mail]>
Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>

kernel/trace/fprobe.c

···
 
 	if (unlikely(kprobe_running())) {
 		fp->nmissed++;
-		return;
+		goto recursion_unlock;
 	}
 
 	kprobe_busy_begin();
 	__fprobe_handler(ip, parent_ip, ops, fregs);
 	kprobe_busy_end();
+
+recursion_unlock:
 	ftrace_test_recursion_unlock(bit);
 }