Add a new configfs attribute for disabling zone write locking. Tests
show a performance of 250 K IOPS with no I/O scheduler, 6 K IOPS with
mq-deadline and write locking enabled and 123 K IOPS with mq-deadline
and write locking disabled. This shows that disabling write locking
results in about 20 times more IOPS for this particular test case.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <redacted>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/block/null_blk/main.c     | 2 ++
 drivers/block/null_blk/null_blk.h | 1 +
 drivers/block/null_blk/zoned.c    | 3 +++
 3 files changed, 6 insertions(+)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 864013019d6b..5c0578137f51 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c

@@ -424,6 +424,7 @@ NULLB_DEVICE_ATTR(zone_capacity, ulong, NULL);
 NULLB_DEVICE_ATTR(zone_nr_conv, uint, NULL);
 NULLB_DEVICE_ATTR(zone_max_open, uint, NULL);
 NULLB_DEVICE_ATTR(zone_max_active, uint, NULL);
+NULLB_DEVICE_ATTR(no_zone_write_lock, bool, NULL);
 NULLB_DEVICE_ATTR(virt_boundary, bool, NULL);
 NULLB_DEVICE_ATTR(no_sched, bool, NULL);
 NULLB_DEVICE_ATTR(shared_tag_bitmap, bool, NULL);

@@ -569,6 +570,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
        &nullb_device_attr_zone_max_active,
        &nullb_device_attr_zone_readonly,
        &nullb_device_attr_zone_offline,
+       &nullb_device_attr_no_zone_write_lock,
        &nullb_device_attr_virt_boundary,
        &nullb_device_attr_no_sched,
        &nullb_device_attr_shared_tag_bitmap,

diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index 929f659dd255..b521096bcc3f 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h

@@ -117,6 +117,7 @@ struct nullb_device {
        bool memory_backed; /* if data is stored in memory */
        bool discard; /* if support discard */
        bool zoned; /* if device is zoned */
+       bool no_zone_write_lock;
        bool virt_boundary; /* virtual boundary on/off for the device */
        bool no_sched; /* no IO scheduler for the device */
        bool shared_tag_bitmap; /* use hostwide shared tags */

diff --git a/drivers/block/null_blk/zoned.c b/drivers/block/null_blk/zoned.c
index 55c5b48bc276..31c8364a63e9 100644
--- a/drivers/block/null_blk/zoned.c
+++ b/drivers/block/null_blk/zoned.c

@@ -96,6 +96,9 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)

        spin_lock_init(&dev->zone_res_lock);

+       if (dev->no_zone_write_lock)
+               blk_queue_flag_set(QUEUE_FLAG_NO_ZONE_WRITE_LOCK, q);
+
        if (dev->zone_nr_conv >= dev->nr_zones) {
                dev->zone_nr_conv = dev->nr_zones - 1;
                pr_info("changed the number of conventional zones to %u",