【OLK-5.10】block, bfq: switch 'bfqg->ref' to use atomic refcount apis

The updating of 'bfqg->ref' should be protected by 'bfqd->lock', however,
during code review, we found that bfq_pd_free() update 'bfqg->ref'
without holding the lock, which is problematic:

bfq_pd_free() triggered by removing cgroup is called asynchronously;
bfqq will grab bfqg reference, and exit bfqq will drop the reference,
which can concurrent with 1).

Unfortunately, 'bfqd->lock' can't be held here because 'bfqd' might already
be freed in bfq_pd_free(). Fix the problem by using atomic refcount apis.

Signed-off-by: Yu Kuai yukuai3@huawei.com
Reviewed-by: Jan Kara jack@suse.cz
Link: https://lore.kernel.org/r/20230103084755.1256479-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe axboe@kernel.dk

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【OLK-5.10】block, bfq: switch 'bfqg->ref' to use atomic refcount apis

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