[PATCH v2 0/2] Introduce bdev_zone_is_seq()

[PATCH v2 0/2] Introduce bdev_zone_is_seq()

[Damien Le Moal]

Allow file systems to safely access a block device gendisk bitmap of
conventional zones to determine a zone type by:
1) Patch 1 - changing the gendisk conv_zones_bitmap to be RCU protected
2) Patch 2 - Introducing the helper function bdev_zone_is_seq()

This is in preparation for use in btrfs to remove the btrfs-managed
bitmap of conventional zones and in zoned support for xfs.

Changes from v1:
 - Use rcu_dereference() in disk_zone_is_conv() (patch 1) and rebase
   patch 2, as suggested by Christoph.

Damien Le Moal (2):
  block: RCU protect disk->conv_zones_bitmap
  block: Add a public bdev_zone_is_seq() helper

 block/blk-zoned.c      | 42 ++++++++++++++++++++++++------------------
 include/linux/blkdev.h | 29 ++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 19 deletions(-)

-- 
2.47.0

[PATCH v2 1/2] block: RCU protect disk->conv_zones_bitmap

[Damien Le Moal]

Ensure that a disk revalidation changing the conventional zones bitmap
of a disk does not cause invalid memory references when using the
disk_zone_is_conv() helper by RCU protecting the disk->conv_zones_bitmap
pointer.

disk_zone_is_conv() is modified to operate under the RCU read lock and
the function disk_set_conv_zones_bitmap() is added to update a disk
conv_zones_bitmap pointer using rcu_replace_pointer() with the disk
zone_wplugs_lock spinlock held.

disk_free_zone_resources() is modified to call
disk_update_zone_resources() with a NULL bitmap pointer to free the disk
conv_zones_bitmap. disk_set_conv_zones_bitmap() is also used in
disk_update_zone_resources() to set the new (revalidated) bitmap and
free the old one.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 block/blk-zoned.c      | 43 ++++++++++++++++++++++++++++++------------
 include/linux/blkdev.h |  2 +-
 2 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index a287577d1ad6..bf4458b11720 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -350,9 +350,15 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, blk_mode_t mode,
 
 static inline bool disk_zone_is_conv(struct gendisk *disk, sector_t sector)
 {
-	if (!disk->conv_zones_bitmap)
-		return false;
-	return test_bit(disk_zone_no(disk, sector), disk->conv_zones_bitmap);
+	unsigned long *bitmap;
+	bool is_conv;
+
+	rcu_read_lock();
+	bitmap = rcu_dereference(disk->conv_zones_bitmap);
+	is_conv = bitmap && test_bit(disk_zone_no(disk, sector), bitmap);
+	rcu_read_unlock();
+
+	return is_conv;
 }
 
 static bool disk_zone_is_last(struct gendisk *disk, struct blk_zone *zone)
@@ -1455,6 +1461,24 @@ static void disk_destroy_zone_wplugs_hash_table(struct gendisk *disk)
 	disk->zone_wplugs_hash_bits = 0;
 }
 
+static unsigned int disk_set_conv_zones_bitmap(struct gendisk *disk,
+					       unsigned long *bitmap)
+{
+	unsigned int nr_conv_zones = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&disk->zone_wplugs_lock, flags);
+	if (bitmap)
+		nr_conv_zones = bitmap_weight(bitmap, disk->nr_zones);
+	bitmap = rcu_replace_pointer(disk->conv_zones_bitmap, bitmap,
+				     lockdep_is_held(&disk->zone_wplugs_lock));
+	spin_unlock_irqrestore(&disk->zone_wplugs_lock, flags);
+
+	kfree_rcu_mightsleep(bitmap);
+
+	return nr_conv_zones;
+}
+
 void disk_free_zone_resources(struct gendisk *disk)
 {
 	if (!disk->zone_wplugs_pool)
@@ -1478,8 +1502,7 @@ void disk_free_zone_resources(struct gendisk *disk)
 	mempool_destroy(disk->zone_wplugs_pool);
 	disk->zone_wplugs_pool = NULL;
 
-	bitmap_free(disk->conv_zones_bitmap);
-	disk->conv_zones_bitmap = NULL;
+	disk_set_conv_zones_bitmap(disk, NULL);
 	disk->zone_capacity = 0;
 	disk->last_zone_capacity = 0;
 	disk->nr_zones = 0;
@@ -1538,17 +1561,15 @@ static int disk_update_zone_resources(struct gendisk *disk,
 				      struct blk_revalidate_zone_args *args)
 {
 	struct request_queue *q = disk->queue;
-	unsigned int nr_seq_zones, nr_conv_zones = 0;
+	unsigned int nr_seq_zones, nr_conv_zones;
 	unsigned int pool_size;
 	struct queue_limits lim;
 
 	disk->nr_zones = args->nr_zones;
 	disk->zone_capacity = args->zone_capacity;
 	disk->last_zone_capacity = args->last_zone_capacity;
-	swap(disk->conv_zones_bitmap, args->conv_zones_bitmap);
-	if (disk->conv_zones_bitmap)
-		nr_conv_zones = bitmap_weight(disk->conv_zones_bitmap,
-					      disk->nr_zones);
+	nr_conv_zones =
+		disk_set_conv_zones_bitmap(disk, args->conv_zones_bitmap);
 	if (nr_conv_zones >= disk->nr_zones) {
 		pr_warn("%s: Invalid number of conventional zones %u / %u\n",
 			disk->disk_name, nr_conv_zones, disk->nr_zones);
@@ -1817,8 +1838,6 @@ int blk_revalidate_disk_zones(struct gendisk *disk)
 		disk_free_zone_resources(disk);
 	blk_mq_unfreeze_queue(q);
 
-	kfree(args.conv_zones_bitmap);
-
 	return ret;
 }
 EXPORT_SYMBOL_GPL(blk_revalidate_disk_zones);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6d1413bd69a5..5687eb2a019c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -195,7 +195,7 @@ struct gendisk {
 	unsigned int		nr_zones;
 	unsigned int		zone_capacity;
 	unsigned int		last_zone_capacity;
-	unsigned long		*conv_zones_bitmap;
+	unsigned long __rcu	*conv_zones_bitmap;
 	unsigned int            zone_wplugs_hash_bits;
 	spinlock_t              zone_wplugs_lock;
 	struct mempool_s	*zone_wplugs_pool;
-- 
2.47.0

[PATCH v2 2/2] block: Add a public bdev_zone_is_seq() helper

[Damien Le Moal]

Turn the private disk_zone_is_conv() function in blk-zoned.c into a
public and documented bdev_zone_is_seq() helper with the inverse
polarity of the original function, also adding a check for non-zoned
devices so that all file systems can use the helper, even with a regular
block device.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 block/blk-zoned.c      | 17 ++---------------
 include/linux/blkdev.h | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index bf4458b11720..797a5d30ac01 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -348,19 +348,6 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, blk_mode_t mode,
 	return ret;
 }
 
-static inline bool disk_zone_is_conv(struct gendisk *disk, sector_t sector)
-{
-	unsigned long *bitmap;
-	bool is_conv;
-
-	rcu_read_lock();
-	bitmap = rcu_dereference(disk->conv_zones_bitmap);
-	is_conv = bitmap && test_bit(disk_zone_no(disk, sector), bitmap);
-	rcu_read_unlock();
-
-	return is_conv;
-}
-
 static bool disk_zone_is_last(struct gendisk *disk, struct blk_zone *zone)
 {
 	return zone->start + zone->len >= get_capacity(disk);
@@ -715,7 +702,7 @@ static bool blk_zone_wplug_handle_reset_or_finish(struct bio *bio,
 	struct blk_zone_wplug *zwplug;
 
 	/* Conventional zones cannot be reset nor finished. */
-	if (disk_zone_is_conv(disk, sector)) {
+	if (!bdev_zone_is_seq(bio->bi_bdev, sector)) {
 		bio_io_error(bio);
 		return true;
 	}
@@ -969,7 +956,7 @@ static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
 	}
 
 	/* Conventional zones do not need write plugging. */
-	if (disk_zone_is_conv(disk, sector)) {
+	if (!bdev_zone_is_seq(bio->bi_bdev, sector)) {
 		/* Zone append to conventional zones is not allowed. */
 		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
 			bio_io_error(bio);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 5687eb2a019c..ac5aad7ca22f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1380,6 +1380,33 @@ static inline bool bdev_is_zone_start(struct block_device *bdev,
 	return bdev_offset_from_zone_start(bdev, sector) == 0;
 }
 
+/**
+ * bdev_zone_is_seq - check if a sector belongs to a sequential write zone
+ * @bdev:	block device to check
+ * @sector:	sector number
+ *
+ * Check if @sector on @bdev is contained in a sequential write required zone.
+ */
+static inline bool bdev_zone_is_seq(struct block_device *bdev, sector_t sector)
+{
+	bool is_seq = false;
+
+#if IS_ENABLED(CONFIG_BLK_DEV_ZONED)
+	if (bdev_is_zoned(bdev)) {
+		struct gendisk *disk = bdev->bd_disk;
+		unsigned long *bitmap;
+
+		rcu_read_lock();
+		bitmap = rcu_dereference(disk->conv_zones_bitmap);
+		is_seq = !bitmap ||
+			!test_bit(disk_zone_no(disk, sector), bitmap);
+		rcu_read_unlock();
+	}
+#endif
+
+	return is_seq;
+}
+
 static inline int queue_dma_alignment(const struct request_queue *q)
 {
 	return q->limits.dma_alignment;
-- 
2.47.0

Re: [PATCH v2 1/2] block: RCU protect disk->conv_zones_bitmap

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 2/2] block: Add a public bdev_zone_is_seq() helper

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 0/2] Introduce bdev_zone_is_seq()

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
for the series

Re: [PATCH v2 0/2] Introduce bdev_zone_is_seq()

[Jens Axboe]

On Thu, 07 Nov 2024 15:42:58 +0900, Damien Le Moal wrote:
> Allow file systems to safely access a block device gendisk bitmap of
> conventional zones to determine a zone type by:
> 1) Patch 1 - changing the gendisk conv_zones_bitmap to be RCU protected
> 2) Patch 2 - Introducing the helper function bdev_zone_is_seq()
> 
> This is in preparation for use in btrfs to remove the btrfs-managed
> bitmap of conventional zones and in zoned support for xfs.
> 
> [...]

Applied, thanks!

[1/2] block: RCU protect disk->conv_zones_bitmap
      commit: d7cb6d7414ea1b33536fa6d11805cb8dceec1f97
[2/2] block: Add a public bdev_zone_is_seq() helper
      commit: f3d9bf05140dd242cdc33c431489a853f2bc1b67

Best regards,
-- 
Jens Axboe