[PATCH RFC 3/3] md: Missing decrease active_io for flush io

[Xiao Ni]

If all flush bios finish fast, it doesn't decrease active_io. And it will
stuck when stopping array.

This can be reproduced by lvm2 test shell/integrity-caching.sh.
But it can't reproduce 100%.

Fixes: fa2bbff7b0b4 ("md: synchronize flush io with array reconfiguration")
Signed-off-by: Xiao Ni <x...@redhat.com>
---
 drivers/md/md.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 77e3af7cf6bb..a41bed286fd2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -579,8 +579,12 @@ static void submit_flushes(struct work_struct *ws)
                        rcu_read_lock();
                }
        rcu_read_unlock();
-       if (atomic_dec_and_test(&mddev->flush_pending))
+       if (atomic_dec_and_test(&mddev->flush_pending)) {
+               /* The pair is percpu_ref_get() from md_flush_request() */
+               percpu_ref_put(&mddev->active_io);
+
                queue_work(md_wq, &mddev->flush_work);
+       }
 }
 
 static void md_submit_flush_data(struct work_struct *ws)
-- 
2.32.0 (Apple Git-132)