Re: [PATCH stable 5.10 1/3] block: look up holders by bdev

Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> · Mon, 1 Aug 2022 20:25:27 +0800

Hi, Greg

在 2022/08/01 19:19, Greg KH 写道:
On Fri, Jul 29, 2022 at 02:23:54PM +0800, Yu Kuai wrote:
From: Christoph Hellwig <hch@xxxxxx>

commit 0dbcfe247f22a6d73302dfa691c48b3c14d31c4c upstream.

Invert they way the holder relations are tracked.  This very
slightly reduces the memory overhead for partitioned devices.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
  block/genhd.c             |  3 +++
  fs/block_dev.c            | 31 +++++++++++++++++++------------
  include/linux/blk_types.h |  3 ---
  include/linux/genhd.h     |  4 +++-
  4 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 796baf761202..2b11a2735285 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1760,6 +1760,9 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
  	disk_to_dev(disk)->class = &block_class;
  	disk_to_dev(disk)->type = &disk_type;
  	device_initialize(disk_to_dev(disk));
+#ifdef CONFIG_SYSFS
+	INIT_LIST_HEAD(&disk->slave_bdevs);
+#endif
  	return disk;
  
  out_free_part0:
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 29f020c4b2d0..a202c76fcf7f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -823,9 +823,6 @@ static void init_once(void *foo)
  
  	memset(bdev, 0, sizeof(*bdev));
  	mutex_init(&bdev->bd_mutex);
-#ifdef CONFIG_SYSFS
-	INIT_LIST_HEAD(&bdev->bd_holder_disks);
-#endif
  	bdev->bd_bdi = &noop_backing_dev_info;
  	inode_init_once(&ei->vfs_inode);
  	/* Initialize mutex for freeze. */
@@ -1188,7 +1185,7 @@ EXPORT_SYMBOL(bd_abort_claiming);
  #ifdef CONFIG_SYSFS
  struct bd_holder_disk {
  	struct list_head	list;
-	struct gendisk		*disk;
+	struct block_device	*bdev;
  	int			refcnt;
  };
  
@@ -1197,8 +1194,8 @@ static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
  {
  	struct bd_holder_disk *holder;
  
-	list_for_each_entry(holder, &bdev->bd_holder_disks, list)
-		if (holder->disk == disk)
+	list_for_each_entry(holder, &disk->slave_bdevs, list)
+		if (holder->bdev == bdev)
  			return holder;
  	return NULL;
  }
@@ -1244,9 +1241,13 @@ static void del_symlink(struct kobject *from, struct kobject *to)
  int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  {
  	struct bd_holder_disk *holder;
+	struct block_device *bdev_holder = bdget_disk(disk, 0);
  	int ret = 0;
  
-	mutex_lock(&bdev->bd_mutex);
+	if (WARN_ON_ONCE(!bdev_holder))
+		return -ENOENT;
+
+	mutex_lock(&bdev_holder->bd_mutex);
  
  	WARN_ON_ONCE(!bdev->bd_holder);
  
@@ -1267,7 +1268,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  	}
  
  	INIT_LIST_HEAD(&holder->list);
-	holder->disk = disk;
+	holder->bdev = bdev;
  	holder->refcnt = 1;
  
  	ret = add_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);
@@ -1283,7 +1284,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  	 */
  	kobject_get(bdev->bd_part->holder_dir);
  
-	list_add(&holder->list, &bdev->bd_holder_disks);
+	list_add(&holder->list, &disk->slave_bdevs);
  	goto out_unlock;
  
  out_del:
@@ -1291,7 +1292,8 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  out_free:
  	kfree(holder);
  out_unlock:
-	mutex_unlock(&bdev->bd_mutex);
+	mutex_unlock(&bdev_holder->bd_mutex);
+	bdput(bdev_holder);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(bd_link_disk_holder);
@@ -1309,8 +1311,12 @@ EXPORT_SYMBOL_GPL(bd_link_disk_holder);
  void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
  {
  	struct bd_holder_disk *holder;
+	struct block_device *bdev_holder = bdget_disk(disk, 0);
  
-	mutex_lock(&bdev->bd_mutex);
+	if (WARN_ON_ONCE(!bdev_holder))
+		return;
+
+	mutex_lock(&bdev_holder->bd_mutex);
  
  	holder = bd_find_holder_disk(bdev, disk);
  
@@ -1323,7 +1329,8 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
  		kfree(holder);
  	}
  
-	mutex_unlock(&bdev->bd_mutex);
+	mutex_unlock(&bdev_holder->bd_mutex);
+	bdput(bdev_holder);
  }
  EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
  #endif
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d9b69bbde5cc..1b84ecb34c18 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -29,9 +29,6 @@ struct block_device {
  	void *			bd_holder;
  	int			bd_holders;
  	bool			bd_write_holder;
-#ifdef CONFIG_SYSFS
-	struct list_head	bd_holder_disks;
-#endif
  	struct block_device *	bd_contains;
  	u8			bd_partno;
  	struct hd_struct *	bd_part;
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 03da3f603d30..3e5049a527e6 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -195,7 +195,9 @@ struct gendisk {
  #define GD_NEED_PART_SCAN		0
  	struct rw_semaphore lookup_sem;
  	struct kobject *slave_dir;
-
+#ifdef CONFIG_SYSFS
+	struct list_head	slave_bdevs;
+#endif

This is very different from the upstream version, and forces the change
onto everyone, not just those who had CONFIG_BLOCK_HOLDER_DEPRECATED
enabled like was done in the main kernel tree.

Why force this on all and not just use the same option?

I would need a strong ACK from the original developers and maintainers
of these subsystems before being able to take these into the 5.10 tree.

Yes, I agree that Christoph must take a look first.

What prevents you from just using 5.15 for those systems that run into
these issues?

The null pointer problem is reported by our product(related to dm-
mpath), and they had been using 5.10 for a long time. And switching
kernel for commercial will require lots of work, it's not an option
for now.

Thanks,
Kuai

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