Re: [PATCH 3/8] uprobes: protected uprobe lifetime with SRCU

Andrii Nakryiko
2024-08-05T17:31:48Z

On Mon, Aug 5, 2024 at 7:52 AM Oleg Nesterov <oleg@redhat.com> wrote:
>
> LGTM, just a few notes...
>
> On 07/31, Andrii Nakryiko wrote:
> >
> > @@ -59,6 +61,7 @@ struct uprobe {
> > struct list_head pending_list;
> > struct uprobe_consumer *consumers;
> > struct inode *inode; /* Also hold a ref to inode */
> > + struct rcu_head rcu;
>
> you can probably put the new member into the union with, say, rb_node.

yep, good point, will do

>
> > @@ -1945,9 +1950,14 @@ pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
> > if (!utask)
> > return -ENOMEM;
> >
> > + if (!try_get_uprobe(uprobe))
> > + return -EINVAL;
> > +
>
> a bit off-topic right now, but it seems that we can simply kill
> utask->active_uprobe. We can turn into into "bool has_active_uprobe"
> and copy uprobe->arch into uprobe_task. Lets discuss this later.

I'm going to change this active_uprobe thing to be either refcounted
or SRCU-protected (but with timeout), so I'll need a bit more
structure around this. Let's see how that lands and if we still can
get rid of it, we can discuss.

>
> > @@ -2201,13 +2215,15 @@ static void handle_swbp(struct pt_regs *regs)
> > {
> > struct uprobe *uprobe;
> > unsigned long bp_vaddr;
> > - int is_swbp;
> > + int is_swbp, srcu_idx;
> >
> > bp_vaddr = uprobe_get_swbp_addr(regs);
> > if (bp_vaddr == uprobe_get_trampoline_vaddr())
> > return uprobe_handle_trampoline(regs);
> >
> > - uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
> > + srcu_idx = srcu_read_lock(&uprobes_srcu);
> > +
> > + uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
> > if (!uprobe) {
> > if (is_swbp > 0) {
> > /* No matching uprobe; signal SIGTRAP. */
> > @@ -2223,6 +2239,7 @@ static void handle_swbp(struct pt_regs *regs)
> > */
> > instruction_pointer_set(regs, bp_vaddr);
> > }
> > + srcu_read_unlock(&uprobes_srcu, srcu_idx);
> > return;
>
> Why not
> goto out;
>
> ?
>

Good point, can be goto out, will change.

> Oleg.
>