[Devel] [PATCH RHEL9 COMMIT] dm-qcow2: Stop using err_status_lock

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.0-42.vz9.14.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-42.vz9.14.3
------>
commit f03ea887b5e51cd7b0616299c8769b99d5c15f44
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Wed Mar 2 20:04:13 2022 +0300

    dm-qcow2: Stop using err_status_lock
    
    Instead of using spinlock as mem barrier, use memory barrier instead.
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    Feature: dm-qcow2: block device over QCOW2 files driver
---
 drivers/md/dm-qcow2-cmd.c    | 11 ++++-------
 drivers/md/dm-qcow2-target.c |  1 -
 drivers/md/dm-qcow2.h        |  1 -
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/md/dm-qcow2-cmd.c b/drivers/md/dm-qcow2-cmd.c
index 779c6618e598..7c91daa5af2d 100644
--- a/drivers/md/dm-qcow2-cmd.c
+++ b/drivers/md/dm-qcow2-cmd.c
@@ -41,12 +41,10 @@ static void service_qio_endio(struct qcow2_target *tgt, struct qio *qio,
 			      void *data, blk_status_t status)
 {
 	blk_status_t *status_ptr = data;
-	unsigned long flags;
 
 	if (unlikely(status)) {
-		spin_lock_irqsave(&tgt->err_status_lock, flags);
-		*status_ptr = status;
-		spin_unlock_irqrestore(&tgt->err_status_lock, flags);
+		WRITE_ONCE(*status_ptr, status);
+		smp_wmb(); /* Pairs with smp_rmb() in qcow2_service_iter() */
 	}
 
 	atomic_dec(&tgt->service_qios);
@@ -99,9 +97,8 @@ static int qcow2_service_iter(struct qcow2_target *tgt, struct qcow2 *qcow2,
 
 	wait_event(tgt->service_wq, !atomic_read(&tgt->service_qios));
 	if (!ret) {
-		spin_lock_irq(&tgt->err_status_lock);
-		ret = blk_status_to_errno(service_status);
-		spin_unlock_irq(&tgt->err_status_lock);
+		smp_rmb(); /* Pairs with smp_wmb() in service_qio_endio() */
+		ret = blk_status_to_errno(READ_ONCE(service_status));
 	}
 
 	return ret;
diff --git a/drivers/md/dm-qcow2-target.c b/drivers/md/dm-qcow2-target.c
index 2a29bff42bfe..99a0359391ce 100644
--- a/drivers/md/dm-qcow2-target.c
+++ b/drivers/md/dm-qcow2-target.c
@@ -448,7 +448,6 @@ static struct qcow2_target *alloc_qcow2_target(struct dm_target *ti)
 	}
 
 	init_completion(&tgt->inflight_ref_comp);
-	spin_lock_init(&tgt->err_status_lock);
 	mutex_init(&tgt->ctl_mutex);
 	init_waitqueue_head(&tgt->service_wq);
 	ti->private = tgt;
diff --git a/drivers/md/dm-qcow2.h b/drivers/md/dm-qcow2.h
index 962b767c84b1..14899608b30f 100644
--- a/drivers/md/dm-qcow2.h
+++ b/drivers/md/dm-qcow2.h
@@ -125,7 +125,6 @@ struct qcow2_target {
 	atomic_t service_qios;
 	struct wait_queue_head service_wq;
 
-	spinlock_t err_status_lock;
 	struct mutex ctl_mutex;
 };