fprobes: Add a comment why fprobe_kprobe_handler exits if kprobe is running

Add a comment the reason why fprobe_kprobe_handler() exits if any other
kprobe is running.

Link: https://lore.kernel.org/all/168874788299.159442.2485957441413653858.stgit@devnote2/
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Link: https://lore.kernel.org/all/20230706120916.3c6abf15@gandalf.local.home/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 2571f7f..59321d2 100644 (file)
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -100,6 +100,12 @@ static void fprobe_kprobe_handler(unsigned long ip, unsigned long parent_ip,
                return;
        }
 
+       /*
+        * This user handler is shared with other kprobes and is not expected to be
+        * called recursively. So if any other kprobe handler is running, this will
+        * exit as kprobe does. See the section 'Share the callbacks with kprobes'
+        * in Documentation/trace/fprobe.rst for more information.
+        */
        if (unlikely(kprobe_running())) {
                fp->nmissed++;
                goto recursion_unlock;