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

Oleg Nesterov
2024-09-13T10:58:16Z

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);
}

...
}