[PATCH 1/7] md: Revert fa2bbff7b0b4 ("md: synchronize flush io with array reconfiguration")

[Mikulas Patocka <mpatocka@redhat.com>]

The commit fa2bbff7b0b4 breaks the LVM2 test shell/integrity-caching.sh,
so let's revert it.

sysrq: Show Blocked State
task:lvm             state:D stack:0     pid:8275  tgid:8275  ppid:1373   flags:0x00000002
Call Trace:
 <TASK>
 __schedule+0x228/0x570
 ? __percpu_ref_switch_mode+0xb7/0x1b0
 schedule+0x29/0xa0
 mddev_suspend+0xec/0x1a0 [md_mod]
 ? housekeeping_test_cpu+0x30/0x30
 dm_table_postsuspend_targets+0x34/0x50 [dm_mod]
 __dm_destroy+0x1c5/0x1e0 [dm_mod]
 ? table_clear+0xa0/0xa0 [dm_mod]
 dev_remove+0xd4/0x110 [dm_mod]
 ctl_ioctl+0x2e1/0x570 [dm_mod]
 dm_ctl_ioctl+0x5/0x10 [dm_mod]
 __x64_sys_ioctl+0x85/0xa0
 do_syscall_64+0x5d/0x1a0
 entry_SYSCALL_64_after_hwframe+0x46/0x4e

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: fa2bbff7b0b4 ("md: synchronize flush io with array reconfiguration")

---
 drivers/md/md.c |   21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

Index: linux-2.6/drivers/md/md.c
===================================================================
--- linux-2.6.orig/drivers/md/md.c
+++ linux-2.6/drivers/md/md.c
@@ -543,9 +543,6 @@ static void md_end_flush(struct bio *bio
 	rdev_dec_pending(rdev, mddev);
 
 	if (atomic_dec_and_test(&mddev->flush_pending)) {
-		/* The pair is percpu_ref_get() from md_flush_request() */
-		percpu_ref_put(&mddev->active_io);
-
 		/* The pre-request flush has finished */
 		queue_work(md_wq, &mddev->flush_work);
 	}
@@ -565,7 +562,12 @@ static void submit_flushes(struct work_s
 	rdev_for_each_rcu(rdev, mddev)
 		if (rdev->raid_disk >= 0 &&
 		    !test_bit(Faulty, &rdev->flags)) {
+			/* Take two references, one is dropped
+			 * when request finishes, one after
+			 * we reclaim rcu_read_lock
+			 */
 			struct bio *bi;
+			atomic_inc(&rdev->nr_pending);
 
 			atomic_inc(&rdev->nr_pending);
 			rcu_read_unlock();
@@ -577,6 +579,7 @@ static void submit_flushes(struct work_s
 			atomic_inc(&mddev->flush_pending);
 			submit_bio(bi);
 			rcu_read_lock();
+			rdev_dec_pending(rdev, mddev);
 		}
 	rcu_read_unlock();
 	if (atomic_dec_and_test(&mddev->flush_pending))
@@ -629,18 +632,6 @@ bool md_flush_request(struct mddev *mdde
 	/* new request after previous flush is completed */
 	if (ktime_after(req_start, mddev->prev_flush_start)) {
 		WARN_ON(mddev->flush_bio);
-		/*
-		 * Grab a reference to make sure mddev_suspend() will wait for
-		 * this flush to be done.
-		 *
-		 * md_flush_reqeust() is called under md_handle_request() and
-		 * 'active_io' is already grabbed, hence percpu_ref_is_zero()
-		 * won't pass, percpu_ref_tryget_live() can't be used because
-		 * percpu_ref_kill() can be called by mddev_suspend()
-		 * concurrently.
-		 */
-		WARN_ON(percpu_ref_is_zero(&mddev->active_io));
-		percpu_ref_get(&mddev->active_io);
 		mddev->flush_bio = bio;
 		bio = NULL;
 	}