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blkcg: Restructure blkg_conf_prep() and friends

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We want to support lazy init of rq-qos policies so that iolatency is enabled
lazily on configuration instead of gendisk initialization. The way blkg
config helpers are structured now is a bit awkward for that. Let's
restructure:

* blkcg_conf_open_bdev() is renamed to blkg_conf_open_bdev(). The blkcg_
  prefix was used because the bdev opening step is blkg-independent.
  However, the distinction is too subtle and confuses more than helps. Let's
  switch to blkg prefix so that it's consistent with the type and other
  helper names.

* struct blkg_conf_ctx now remembers the original input string and is always
  initialized by the new blkg_conf_init().

* blkg_conf_open_bdev() is updated to take a pointer to blkg_conf_ctx like
  blkg_conf_prep() and can be called multiple times safely. Instead of
  modifying the double pointer to input string directly,
  blkg_conf_open_bdev() now sets blkg_conf_ctx->body.

* blkg_conf_finish() is renamed to blkg_conf_exit() for symmetry and now
  must be called on all blkg_conf_ctx's which were initialized with
  blkg_conf_init().

Combined, this allows the users to either open the bdev first or do it
altogether with blkg_conf_prep() which will help implementing lazy init of
rq-qos policies.

blkg_conf_init/exit() will also be used implement synchronization against
device removal. This is necessary because iolat / iocost are configured
through cgroupfs instead of one of the files under /sys/block/DEVICE. As
cgroupfs operations aren't synchronized with block layer, the lazy init and
other configuration operations may race against device removal. This patch
makes blkg_conf_init/exit() used consistently for all cgroup-orginating
configurations making them a good place to implement explicit
synchronization.

Users are updated accordingly. No behavior change is intended by this patch.

v2: bfq wasn't updated in v1 causing a build error. Fixed.

v3: Update the description to include future use of blkg_conf_init/exit() as
    synchronization points.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Yu Kuai <yukuai1@huaweicloud.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230413000649.115785-3-tj@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo
2023-04-12 14:06:47 -10:00
committed by Jens Axboe
parent 83462a6c97
commit faffaab289
6 changed files with 128 additions and 79 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
block/blk-throttle.c
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@@ -1368,9 +1368,11 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of,
int ret;
u64 v;
ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
blkg_conf_init(&ctx, buf);
ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, &ctx);
if (ret)
return ret;
goto out_finish;
ret = -EINVAL;
if (sscanf(ctx.body, "%llu", &v) != 1)
@@ -1389,7 +1391,7 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of,
tg_conf_updated(tg, false);
ret = 0;
out_finish:
blkg_conf_finish(&ctx);
blkg_conf_exit(&ctx);
return ret ?: nbytes;
}
@@ -1561,9 +1563,11 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
int ret;
int index = of_cft(of)->private;
ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
blkg_conf_init(&ctx, buf);
ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, &ctx);
if (ret)
return ret;
goto out_finish;
tg = blkg_to_tg(ctx.blkg);
tg_update_carryover(tg);
@@ -1662,7 +1666,7 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
tg->td->limit_valid[LIMIT_LOW]);
ret = 0;
out_finish:
blkg_conf_finish(&ctx);
blkg_conf_exit(&ctx);
return ret ?: nbytes;
}