kprobes: Fix error check when reusing optimized probes

The following commit introduced a bug in one of our error paths:

819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")

it missed to handle the return value of kprobe_optready() as
error-value. In reality, the kprobe_optready() returns a bool
result, so "true" case must be passed instead of 0.

This causes some errors on kprobe boot-time selftests on ARM:

[ ] Beginning kprobe tests...
[ ] Probe ARM code
[ ] kprobe
[ ] kretprobe
[ ] ARM instruction simulation
[ ] Check decoding tables
[ ] Run test cases
[ ] FAIL: test_case_handler not run
[ ] FAIL: Test andge r10, r11, r14, asr r7
[ ] FAIL: Scenario 11
...
[ ] FAIL: Scenario 7
[ ] Total instruction simulation tests=1631, pass=1433 fail=198
[ ] kprobe tests failed

This can happen if an optimized probe is unregistered and next
kprobe is registered on same address until the previous probe
is not reclaimed.

If this happens, a hidden aggregated probe may be kept in memory,
and no new kprobe can probe same address. Also, in that case
register_kprobe() will return "1" instead of minus error value,
which can mislead caller logic.

Signed-off-by: Masami Hiramatsu <[e-mail]>
Cc: Anil S Keshavamurthy <[e-mail]>
Cc: David S . Miller <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Naveen N . Rao <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail] # v5.0+
Fixes: 819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")
Link: http://lkml.kernel.org/r/155530808559.32517.539898325433642204.stgit@devnote2
Signed-off-by: Ingo Molnar <[e-mail]>

kernel/kprobes.c

···
 static int reuse_unused_kprobe(struct kprobe *ap)
 {
 	struct optimized_kprobe *op;
-	int ret;
 
 	/*
 	 * Unused kprobe MUST be on the way of delayed unoptimizing (means
···
 	/* Enable the probe again */
 	ap->flags &= ~KPROBE_FLAG_DISABLED;
 	/* Optimize it again (remove from op->list) */
-	ret = kprobe_optready(ap);
-	if (ret)
-		return ret;
+	if (!kprobe_optready(ap))
+		return -EINVAL;
 
 	optimize_kprobe(ap);
 	return 0;