Re: [PATCH v2 2/3] blk-cgroup: store blkcg in bio instead of blkg
From: Christoph Hellwig <hch@lst.de>
Date: 2026-09-15 06:49:57
Also in:
cgroups, dm-devel, gfs2, linux-block, linux-doc, linux-fsdevel, linux-mm, linux-raid, lkml, llvm
On Sun, Sep 13, 2026 at 02:54:39PM +0800, Yu Kuai wrote:
quoted hunk ↗ jump to hunk
@@ -6243,10 +6245,17 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, bool idle_timer_disabled = false; blk_opf_t cmd_flags; LIST_HEAD(free); #ifdef CONFIG_BFQ_GROUP_IOSCHED + /* + * Pin the blkg used to look up bfqg. If this is the first IO for + * the blkcg on this queue, create the bfqg before holding bfqd->lock. + */ + if (rq->bio && !bio_flagged(rq->bio, BIO_BLKG_REF)) + bio_blkg(rq->bio);
Can rq->bio be NULL here? flush or empty passthrough request should never enter the scheuler.
if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio) bfqg_stats_update_legacy_io(q, rq);
But I guess given that the code below checks it, we should at least be consistent, so I guess it is better to keep it for now.
static inline void dm_bio_record(struct dm_bio_details *bd, struct bio *bio)
{
bd->bi_bdev = bio->bi_bdev;
- bd->bi_flags = bio->bi_flags;
+ /* Restoring an ownership bit cannot recreate the associated reference. */
+ bd->bi_flags = bio->bi_flags & ~(1U << BIO_BLKG_REF);I have a bit of a hard time parsing this, the line also is overly long.