Re: [PATCHv3 1/7] uprobe: Add support for session consumer

[Oleg Nesterov]

On 09/13, Jiri Olsa wrote:
>
> I'm not sure the realloc will help, I feel like we need to allocate return
> consumer for each called handler separately to be safe

How about something like the (pseudo) code below? Note that this way
we do not need uprobe->consumers_cnt. Note also that krealloc() should
be unlikely and it checks ksize() before it does another allocation.

Oleg.

static size_t ri_size(int consumers_cnt)
{
        return sizeof(struct return_instance) +
                      sizeof(struct return_consumer) * consumers_cnt;
}

#define DEF_CNT 4       // arbitrary value

static struct return_instance *alloc_return_instance(void)
{
        struct return_instance *ri;

        ri = kzalloc(ri_size(DEF_CNT), GFP_KERNEL);
        if (!ri)
                return ZERO_SIZE_PTR;

        ri->consumers_cnt = DEF_CNT;
        return ri;
}

static struct return_instance *push_id_cookie(struct return_instance *ri, int 
idx,
                                                __u64 id, __u64 cookie)
{
        if (unlikely(ri == ZERO_SIZE_PTR))
                return ri;

        if (unlikely(idx >= ri->consumers_cnt)) {
                ri->consumers_cnt += DEF_CNT;
                ri = krealloc(ri, ri_size(ri->consumers_cnt), GFP_KERNEL);
                if (!ri) {
                        kfree(ri);
                        return ZERO_SIZE_PTR;
                }
        }

        ri->consumers[idx].id = id;
        ri->consumers[idx].cookie = cookie;
        return ri;
}

static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
{
        ...
        struct return_instance *ri = NULL;
        int push_idx = 0;

        list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, 
rcu_read_lock_trace_held()) {
                __u64 cookie = 0;
                int rc = 0;

                if (uc->handler)
                        rc = uc->handler(uc, regs, &cookie);

                remove &= rc;
                has_consumers = true;

                if (!uc->ret_handler || rc == UPROBE_HANDLER_REMOVE || rc == 2)
                        continue;

                if (!ri)
                        ri = alloc_return_instance();

                // or, better if (rc = UPROBE_HANDLER_I_WANT_MY_COOKIE)
                if (uc->handler))
                        ri = push_id_cookie(ri, push_idx++, uc->id, cookie);
        }

        if (!ZERO_OR_NULL_PTR(ri)) {
                ri->consumers_cnt = push_idx;
                prepare_uretprobe(uprobe, regs, ri);
        }

        ...
}