Re: [External] Re: [PATCH 3/5] cachefiles: resend an open request if the read request's object is closed

[Jia Zhu]

在 2022/10/12 15:53, JeffleXu 写道:
> On 10/11/22 9:15 PM, Jia Zhu wrote:
> > @@ -254,12 +282,18 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
> >   	 * request distribution fair.
> >   	 */
> >   	xa_lock(&cache->reqs);
> > -	req = xas_find_marked(&xas, UINT_MAX, CACHEFILES_REQ_NEW);
> > -	if (!req && cache->req_id_next > 0) {
> > -		xas_set(&xas, 0);
> > -		req = xas_find_marked(&xas, cache->req_id_next - 1, CACHEFILES_REQ_NEW);
> > +retry:
> > +	xas_for_each_marked(&xas, req, xa_max, CACHEFILES_REQ_NEW) {
> > +		if (cachefiles_ondemand_skip_req(req))
> > +			continue;
> > +		break;
> >   	}
> >   	if (!req) {
> > +		if (cache->req_id_next > 0 && xa_max == ULONG_MAX) {
> > +			xas_set(&xas, 0);
> > +			xa_max = cache->req_id_next - 1;
> > +			goto retry;
> > +		}
>
> I would suggest abstracting the "xas_for_each_marked(...,
> CACHEFILES_REQ_NEW)" part into a helper function to avoid the "goto retry".
Hi JingBo,

Thanks for your advice. Are the following revises appropriate？

static struct cachefiles_req *cachefiles_ondemand_select_req(struct 
xa_state *xas, unsigned long xa_max)
{
    struct cachefiles_req *req;
    struct cachefiles_ondemand_info *info;

    xas_for_each_marked(xas, req, xa_max, CACHEFILES_REQ_NEW) {
        if (!req || req->msg.opcode != CACHEFILES_OP_READ)
            return req;
        info = req->object->private;
        if (info->state == CACHEFILES_ONDEMAND_OBJSTATE_close) {
            cachefiles_ondemand_set_object_reopening(req->object);
            queue_work(fscache_wq, &info->work);
            continue;
        } else if (info->state == CACHEFILES_ONDEMAND_OBJSTATE_reopening) {
            continue;
        }
        return req;
    }
    return NULL;
}

...

 xa_lock(&cache->reqs);
    req = cachefiles_ondemand_select_req(&xas, ULONG_MAX);
    if (!req && cache->req_id_next > 0) {
        xas_set(&xas, 0);
        req = cachefiles_ondemand_select_req(&xas, cache->req_id_next - 1);
    }
    if (!req) {
        xa_unlock(&cache->reqs);
        return 0;
    }
> > @@ -392,8 +434,16 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object,
> >   	wake_up_all(&cache->daemon_pollwq);
> >   	wait_for_completion(&req->done);
> >   	ret = req->error;
> > +	kfree(req);
> > +	return ret;
> >   out:
> >   	kfree(req);
> > +	/* Reset the object to close state in error handling path.
> > +	 * If error occurs after creating the anonymous fd,
> > +	 * cachefiles_ondemand_fd_release() will set object to close.
> > +	 */
> > +	if (opcode == CACHEFILES_OP_OPEN)
> > +		cachefiles_ondemand_set_object_close(req->object);
>
> This may cause use-after-free since @req has been freed.
Thanks for catching this, I'll fix it in next version.
>