fprobe: Fix to ensure the number of active retprobes is not zero

The number of active retprobes can be zero but it is not acceptable,
so return EINVAL error if detected.

Link: https://lore.kernel.org/all/169750018550.186853.11198884812017796410.stgit@devnote2/

Reported-by: wuqiang.matt <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: 5b0ab78 ("fprobe: Add exit_handler support")
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>

Author: mhiramat

kernel/trace/fprobe.c

@@ -189,7 +189,7 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
 {
 	int i, size;
 
-	if (num < 0)
+	if (num <= 0)
 		return -EINVAL;
 
 	if (!fp->exit_handler) {
@@ -202,8 +202,8 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
 		size = fp->nr_maxactive;
 	else
 		size = num * num_possible_cpus() * 2;
-	if (size < 0)
-		return -E2BIG;
+	if (size <= 0)
+		return -EINVAL;
 
 	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
 	if (!fp->rethook)