linux-kernel - [PATCH v2 1/1] null_blk: synchronization fix for zoned device

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Date:   Mon, 28 Sep 2020 15:25:49 +0530
From:   Kanchan Joshi <joshi.k@...sung.com>
To:     axboe@...nel.dk, Damien.LeMoal@....com
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        stable@...r.kernel.org, selvakuma.s1@...sung.com,
        nj.shetty@...sung.com, javier.gonz@...sung.com,
        Kanchan Joshi <joshi.k@...sung.com>
Subject: [PATCH v2 1/1] null_blk: synchronization fix for zoned device

Parallel write,read,zone-mgmt operations accessing/altering zone state
and write-pointer may get into race. Avoid the situation by using a new
spinlock for zoned device.
Concurrent zone-appends (on a zone) returning same write-pointer issue
is also avoided using this lock.

Fixes: e0489ed5daeb ("null_blk: Support REQ_OP_ZONE_APPEND")
Signed-off-by: Kanchan Joshi <joshi.k@...sung.com>
---
 drivers/block/null_blk.h       |  1 +
 drivers/block/null_blk_zoned.c | 22 ++++++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h
index daed4a9c3436..28099be50395 100644
--- a/drivers/block/null_blk.h
+++ b/drivers/block/null_blk.h
@@ -44,6 +44,7 @@ struct nullb_device {
 	unsigned int nr_zones;
 	struct blk_zone *zones;
 	sector_t zone_size_sects;
+	spinlock_t zone_lock;
 
 	unsigned long size; /* device size in MB */
 	unsigned long completion_nsec; /* time in ns to complete a request */
diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
index 3d25c9ad2383..e8d8b13aaa5a 100644
--- a/drivers/block/null_blk_zoned.c
+++ b/drivers/block/null_blk_zoned.c
@@ -45,6 +45,7 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
 	if (!dev->zones)
 		return -ENOMEM;
 
+	spin_lock_init(&dev->zone_lock);
 	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",
@@ -131,8 +132,11 @@ int null_report_zones(struct gendisk *disk, sector_t sector,
 		 * So use a local copy to avoid corruption of the device zone
 		 * array.
 		 */
+		spin_lock_irq(&dev->zone_lock);
 		memcpy(&zone, &dev->zones[first_zone + i],
 		       sizeof(struct blk_zone));
+		spin_unlock_irq(&dev->zone_lock);
+
 		error = cb(&zone, i, data);
 		if (error)
 			return error;
@@ -277,18 +281,28 @@ static blk_status_t null_zone_mgmt(struct nullb_cmd *cmd, enum req_opf op,
 blk_status_t null_process_zoned_cmd(struct nullb_cmd *cmd, enum req_opf op,
 				    sector_t sector, sector_t nr_sectors)
 {
+	blk_status_t sts;
+	struct nullb_device *dev = cmd->nq->dev;
+
+	spin_lock_irq(&dev->zone_lock);
 	switch (op) {
 	case REQ_OP_WRITE:
-		return null_zone_write(cmd, sector, nr_sectors, false);
+		sts = null_zone_write(cmd, sector, nr_sectors, false);
+		break;
 	case REQ_OP_ZONE_APPEND:
-		return null_zone_write(cmd, sector, nr_sectors, true);
+		sts = null_zone_write(cmd, sector, nr_sectors, true);
+		break;
 	case REQ_OP_ZONE_RESET:
 	case REQ_OP_ZONE_RESET_ALL:
 	case REQ_OP_ZONE_OPEN:
 	case REQ_OP_ZONE_CLOSE:
 	case REQ_OP_ZONE_FINISH:
-		return null_zone_mgmt(cmd, op, sector);
+		sts = null_zone_mgmt(cmd, op, sector);
+		break;
 	default:
-		return null_process_cmd(cmd, op, sector, nr_sectors);
+		sts = null_process_cmd(cmd, op, sector, nr_sectors);
 	}
+	spin_unlock_irq(&dev->zone_lock);
+
+	return sts;
 }
-- 
2.25.1