On Thu, Jul 11, 2024 at 06:06:53PM +0200, Oleg Nesterov wrote: > I'll try to actually apply the whole series and read the code tomorrow. > Right now I can't understand this change... Just one question for now. > > On 07/11, Peter Zijlstra wrote: > > > > @@ -1956,11 +1960,13 @@ static void prepare_uretprobe(struct upr > > * attack from user-space. > > */ > > uprobe_warn(current, "handle tail call"); > > - goto err_uprobe; > > + goto err_mem; > > } > > orig_ret_vaddr = utask->return_instances->orig_ret_vaddr; > > } > > > > + ri->srcu_idx = __srcu_read_lock(&uretprobes_srcu); > > + ri->uprobe = uprobe; > > It seems that, if we race with _unregister, this __srcu_read_lock() > can happen after call_srcu(uprobes_srcu, uprobe, uprobe_free_stage1) > was already called... > > In this case read_lock "has no effect" in that uprobe_free_stage1() > can run before free_ret_instance() does srcu_read_unlock(ri->srcu_idx). > > Perhaps it is fine, uprobe_free_stage1() does another call_srcu(), > but somehow I got lost. > > Could you re-check this logic? Most probably I missed something, but still...
handle_swbp() guard(srcu)(&uprobes_srcu); handle_chain(); prepare_uretprobe() __srcu_read_lock(&uretprobe_srcu); vs uprobe_free_stage2 kfree(uprobe) uprobe_free_stage1 call_srcu(&uretprobe_srcu, &uprobe->rcu, uprobe_free_stage2); put_uprobe() if (refcount_dec_and_test) call_srcu(&uprobes_srcu, &uprobe->rcu, uprobe_free_stage1); So my thinking was since we take uretprobe_srcu *inside* uprobe_srcu, this reference must be visible before we execute stage1, and as such stage2 cannot complete prematurely.