Once there is a heavy IO load, so many encrypt/decrypt work will occupy
all of the cpu, which may lead to the poor performance for other service.
So the improved visibility and controls over dm-crypt workqueues, as
was offered with commit a2b8b2d9 ("dm crypt: export sysfs of
kcryptd workqueue"), seems necessary. By exporting dm-crypt's
workqueues in sysfs, the entry like cpumask/max_active and so on can
help us to limit the CPU usage for encrypt/decrypt work.

However, commit a2b8b2d9 did not consider that DM table reload
will call .ctr before .dtr, so the reload for dm-crypt failed because
the same sysfs name was present. This was the original need for commit
48b0777c ("Revert "dm crypt: export sysfs of kcryptd workqueue"").

Reintroduce the use of WQ_SYSFS, and use it for both the IO and crypt
workqueues, but make the workqueue names include a unique id (via ida)
to allow both old and new sysfs entries to coexist.
Signed-off-by: yangerkun <yangerkun@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>