I don't see anything wrong after a quick glance, but I don't
really understand the UPROBE_HANDLER_IGNORE logic, see below.
On 09/17, Jiri Olsa wrote:
>
> + * UPROBE_HANDLER_IWANTMYCOOKIE
> + * - Store cookie and pass it to ret_handler (if defined).
Cough ;) yes it was me who used this name in the previous discussion, but maybe
UPROBE_HANDLER_COOKIE
will look a bit better? Feel free to ignore.
> static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
...
> + if (!uc->ret_handler || rc == UPROBE_HANDLER_REMOVE)
> + continue;
> +
> + /*
> + * If alloc_return_instance and push_consumer fail, the return
> probe
> + * won't be prepared, but we'll finish to execute all entry
> handlers.
> + *
> + * We need to store handler's return value in case the return
> uprobe
> + * gets installed and contains consumers that need to be
> ignored.
> + */
> + if (!ri)
> + ri = alloc_return_instance();
> +
> + if (rc == UPROBE_HANDLER_IWANTMYCOOKIE || rc ==
> UPROBE_HANDLER_IGNORE)
> + ri = push_consumer(ri, push_idx++, uc->id, cookie, rc);
So this code allocates ri (which implies prepare_uretprobe!) and calls
push_consumer()
even if rc == UPROBE_HANDLER_IGNORE.
Why? The comment in uprobes.h says:
UPROBE_HANDLER_IGNORE
- Ignore ret_handler callback for this consumer
but the ret_handler callback won't be ignored?
To me this code should do:
if (!uc->ret_handler || UPROBE_HANDLER_REMOVE ||
UPROBE_HANDLER_IGNORE)
continue;
if (!ri)
ri = alloc_return_instance();
if (rc == UPROBE_HANDLER_IWANTMYCOOKIE)
ri = push_consumer(...);
And,
> handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
...
> list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
> srcu_read_lock_held(&uprobes_srcu)) {
> + ric = return_consumer_find(ri, &ric_idx, uc->id);
> + if (ric && ric->rc == UPROBE_HANDLER_IGNORE)
> + continue;
> if (uc->ret_handler)
> - uc->ret_handler(uc, ri->func, regs);
> + uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie
> : NULL);
> }
the UPROBE_HANDLER_IGNORE check above and the new ric->rc member should die,
if (!uc->ret_handler)
continue;
ric = return_consumer_find(...);
uc->ret_handler(..., ric ? &ric->cookie : NULL);
as we have already discussed, the session ret_handler(data) can simply do
// my ->handler() wasn't called or it didn't return
// UPROBE_HANDLER_IWANTMYCOOKIE
if (!data)
return;
at the start.
Could you explain why this can't work?
Oleg.
