[PATCH v2 3/4] kprobes: Re-optimize blocked sibling probe when cooling finishes

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

When an optimized kprobe is disabled (for example, to arm a new kprobe
in its jump-optimized instruction range), its jump is replaced with a
breakpoint (or disarmed) and the probe is placed on the cooling list
until the Tasks RCU grace period completes. While the disabled probe is
still on the cooling list, any sibling probe whose jump range covers
this probe's address cannot be optimized because can_optimize() sees the
not-yet-disarmed probe via get_kprobe().

In optprobe_finalize_generation(), when a disabled probe on cooling_list
finishes cooling and transitions to safely disarmed (list_del_init()),
check whether an optimized sibling probe covers op->kp.addr via
get_optimized_kprobe() and re-queue it for optimization, matching the
freeing_list path in do_free_cleaned_kprobes().

Fixes: 06e0d3b89da1 ("kprobes: Make optprobe optimizer multi-generational and asynchronous")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v2:
 - Drop the unoptimize_kprobe() and reuse_unused_kprobe() hunks which
   were superseded by commits 0be7a931c5e4 and 1ffd6efb1b58 in
   probes/fixes.
 - Drop the kill_optimized_kprobe() cooling deferral since kill_kprobe()
   runs at MODULE_STATE_GOING when no tasks execute the module text.
---
 kernel/kprobes.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c0637302eeae..88601ecc4e48 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -729,10 +729,17 @@ static void optprobe_finalize_generation(struct optprobe_generation *gen)
 			list_move(&op->list, &optprobe_gens[optprobe_cur_gen].freeing_list);
 			kick_kprobe_optimizer();
 		} else {
+			struct kprobe *_p;
+
 			/* Still in use; now safely disarmed */
 			list_del_init(&op->list);
-			if (!kprobe_disabled(&op->kp))
+			if (!kprobe_disabled(&op->kp)) {
 				optimize_kprobe(&op->kp);
+			} else {
+				_p = get_optimized_kprobe(op->kp.addr);
+				if (unlikely(_p))
+					optimize_kprobe(_p);
+			}
 		}
 	}