blkcg: update blkg_lookup_create() to do locking
To know when to create a blkg, the general pattern is to do a blkg_lookup() and if that fails, lock and do the lookup again, and if that fails finally create. It doesn't make much sense for everyone who wants to do creation to write this themselves. This changes blkg_lookup_create() to do locking and implement this pattern. The old blkg_lookup_create() is renamed to __blkg_lookup_create(). If a call site wants to do its own error handling or already owns the queue lock, they can use __blkg_lookup_create(). This will be used in upcoming patches. Signed-off-by: NDennis Zhou <dennis@kernel.org> Reviewed-by: NJosef Bacik <josef@toxicpanda.com> Acked-by: NTejun Heo <tj@kernel.org> Reviewed-by: NLiu Bo <bo.liu@linux.alibaba.com> Signed-off-by: NJens Axboe <axboe@kernel.dk>
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