On Thu, 27 Aug 2020 18:12:40 +0200 Peter Zijlstra <pet...@infradead.org> wrote:
> +static void invalidate_rp_inst(struct task_struct *t, struct kretprobe *rp) > +{ > + struct invl_rp_ipi iri = { > + .task = t, > + .rp = rp, > + .done = false > + }; > + > + for (;;) { > + if (try_invoke_on_locked_down_task(t, __invalidate_rp_inst, rp)) > + return; > + > + smp_call_function_single(task_cpu(t), __invalidate_rp_ipi, > &iri, 1); > + if (iri.done) > + return; > + } Hmm, what about making a status place holder and point it from each instance to tell it is valid or not? struct kretprobe_holder { atomic_t refcnt; struct kretprobe *rp; }; struct kretprobe { ... struct kretprobe_holder *rph; // allocate at register ... }; struct kretprobe_instance { ... struct kretprobe_holder *rph; // free if refcnt == 0 ... }; cleanup_rp_inst(struct kretprobe *rp) { rp->rph->rp = NULL; } kretprobe_trampoline_handler() { ... rp = READ_ONCE(ri->rph-rp); if (likely(rp)) { // call rp->handler } else rcu_call(ri, free_rp_inst_rcu); ... } free_rp_inst_rcu() { if (!atomic_dec_return(ri->rph->refcnt)) kfree(ri->rph); kfree(ri); } This increase kretprobe_instance a bit, but make things simpler. (and still keep lockless, atomic op is in the rcu callback). Thank you, -- Masami Hiramatsu <mhira...@kernel.org>