On Wed, 30 Sep 2026 13:00:18 +0000 [email protected] wrote: > Thank you for your contribution! Sashiko AI review found 1 potential > issue(s) to consider: > - [High] kprobes: double free/list corruption via double > hlist_del_rcu() on freeing_list -- > > commit 713397faac31184a877c512a3215f1d8fc48a2f8 > Author: Masami Hiramatsu (Google) <[email protected]> > Subject: kprobes: Make optprobe optimizer multi-generational and > asynchronous > > This commit replaces synchronize_rcu_tasks() with call_rcu_tasks() by > introducing a multi-generational ring buffer. The kprobe optimizer now > unoptimizes probes and defers their cleanup asynchronously. > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > index 4edd8ca5c6578..33523e9beb884 100644 > > --- a/kernel/kprobes.c > > +++ b/kernel/kprobes.c > > [ ... ] > > > @@ -624,67 +696,145 @@ static void do_free_cleaned_kprobes(void) > > > > static void kick_kprobe_optimizer(void); > > > > -/* Kprobe jump optimizer */ > > -static void kprobe_optimizer(void) > > +static void optprobe_generation_rcu_cb(struct rcu_head *rcu) > > { > > - guard(mutex)(&kprobe_mutex); > > + struct optprobe_generation *gen; > > + > > + gen = container_of(rcu, struct optprobe_generation, rcu); > > + WRITE_ONCE(gen->ready, true); > > + wake_up(&kprobe_optimizer_wait); > > +} > > + > > +static void optprobe_finalize_generation(struct > > optprobe_generation *gen) +{ > > + struct optimized_kprobe *op, *tmp; > > + > > + lockdep_assert_held(&kprobe_mutex); > > > > scoped_guard(cpus_read_lock) { > > guard(mutex)(&text_mutex); > > > > - /* > > - * Step 1: Unoptimize kprobes and collect cleaned > > (unused and disarmed) > > - * kprobes before waiting for quiesence period. > > - */ > > - do_unoptimize_kprobes(); > > + /* Optimization never be done when disarmed */ > > + if (!kprobes_all_disarmed && > > kprobes_allow_optimization && > > + !list_empty(&gen->optimizing_list)) > > + > > arch_optimize_kprobes(&gen->optimizing_list); > > + } > > + > > + /* Free cleaned kprobes after quiescence period */ > > + do_free_cleaned_kprobes(&gen->freeing_list); > > + > > + /* Finalize unoptimized kprobes whose quiescence period > > completed */ > > + list_for_each_entry_safe(op, tmp, &gen->cooling_list, > > list) { > > + if (kprobe_unused(&op->kp)) { > > + /* > > + * Unregistered while quiescence period > > was in flight. > > + * Remove from hash list and move to > > cur_gen's freeing list. > > + */ > > + hlist_del_rcu(&op->kp.hlist); > > + list_move(&op->list, > > &optprobe_gens[optprobe_cur_gen].freeing_list); > > [Severity: High] > Does this code risk list corruption via a double free? > > If a kprobe in the cooling_list becomes unused and is unhashed here, > it is moved to the current generation's freeing_list. > > When this current generation is later dispatched, > do_unoptimize_kprobes() will iterate over its freeing_list (passed as > free_list): > > kernel/kprobes.c:do_unoptimize_kprobes() { > ... > list_for_each_entry_safe(op, tmp, free_list, list) { > ... > if (kprobe_unused(&op->kp)) { > hlist_del_rcu(&op->kp.hlist); > } > ... > } > > Will this unconditionally call hlist_del_rcu() a second time on the > same probe, causing a regression by dereferencing LIST_POISON2?
Oops, good catch! Since there is no reason to remove it from hash in optprobe_finalize_generation() (it can be reused), I will drop the hlist_del_rcu() from there. Thanks! -- Masami Hiramatsu (Google) <[email protected]>
