dm cache policy smq: ensure IO doesn't prevent cleaner policy progress

stable inclusion
from stable-v5.10.190
commit c0f2b2b020961f1346c8f07e9de43e6cca48726a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I928UI

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0f2b2b020961f1346c8f07e9de43e6cca48726a



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commit 1e4ab7b4 upstream.

When using the cleaner policy to decommission the cache, there is
never any writeback started from the cache as it is constantly delayed
due to normal I/O keeping the device busy. Meaning @idle=false was
always being passed to clean_target_met()

Fix this by adding a specific 'cleaner' flag that is set when the
cleaner policy is configured. This flag serves to always allow the
cleaner's writeback work to be queued until the cache is
decommissioned (even if the cache isn't idle).

Reported-by: David Jeffery <djeffery@redhat.com>
Fixes: b29d4986 ("dm cache: significant rework to leverage dm-bio-prison-v2")
Cc: stable@vger.kernel.org
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>