Hello Dan,
On Wed, Feb 05, 2020 at 02:33:48PM -0800, Dan Schatzberg wrote:
> @@ -1925,14 +1990,13 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
> }
>
> /* always use the first bio's css */
> + cmd->blk_css = NULL;
> #ifdef CONFIG_BLK_CGROUP
> - if (cmd->use_aio && rq->bio && rq->bio->bi_blkg) {
> - cmd->css = &bio_blkcg(rq->bio)->css;
> - css_get(cmd->css);
> - } else
> + if (rq->bio && rq->bio->bi_blkg)
> + cmd->blk_css = &bio_blkcg(rq->bio)->css;
> #endif
> - cmd->css = NULL;
> - kthread_queue_work(&lo->worker, &cmd->work);
> +
> + loop_queue_work(lo, cmd);
>
> return BLK_STS_OK;
> }
> @@ -1942,6 +2006,9 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
> struct request *rq = blk_mq_rq_from_pdu(cmd);
> const bool write = op_is_write(req_op(rq));
> struct loop_device *lo = rq->q->queuedata;
> +#ifdef CONFIG_MEMCG
> + struct cgroup_subsys_state *mem_css;
> +#endif
> int ret = 0;
>
> if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) {
> @@ -1949,8 +2016,24 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
> goto failed;
> }
>
> + if (cmd->blk_css) {
> +#ifdef CONFIG_MEMCG
> + mem_css = cgroup_get_e_css(cmd->blk_css->cgroup,
> + &memory_cgrp_subsys);
> + memalloc_use_memcg(mem_cgroup_from_css(mem_css));
> +#endif
> + kthread_associate_blkcg(cmd->blk_css);
> + }
> +
> ret = do_req_filebacked(lo, rq);
> - failed:
> +
> + if (cmd->blk_css) {
> + kthread_associate_blkcg(NULL);
> +#ifdef CONFIG_MEMCG
> + memalloc_unuse_memcg();
> +#endif
cgroup_get_e_css() acquires a reference, it looks like you're missing
a css_put() here.
I also wonder why you look up blk_css and mem_css in separate
places. Since you already renamed cmd->css to cmd->blk_css, can you
also add cmd->mem_css and pair up their lookup and refcounting?
This should make loop_handle_cmd() a bit more straight-forward:
if (cmd->blk_css)
kthread_associate_blkcg(cmd->blk_css);
if (cmd->mem_css)
memalloc_use_memcg(mem_cgroup_from_css(mem_css));
ret = do_req_filebacked(lo, rq);
memalloc_unuse_memcg();
kthread_associate_blkcg(NULL);
All these functions have dummy implementations for !CONFIG_BLK_CGROUP,
!CONFIG_MEMCG etc., so it shouldn't require any additional ifdefs.
