[v3,1/5] btrfs: remove buffer heads from super block reading

Commit Message

Johannes Thumshirn Jan. 27, 2020, 3:59 p.m. UTC

Super-block reading in BTRFS is done using buffer_heads. Buffer_heads have
some drawbacks, like not being able to propagate errors from the lower
layers.

Change the buffer_heads to BIOs and utilize the page cache for the page
allocation. Compared to buffer_heads using BIOs are more lightweight and
we skip several layers of buffer_head code until we either reach the page
cache or build a BIO and submit it to read the blocks from disk.

Signed-off-by: Johannes Thumshirn <[e-mail]>
Reviewed-by: Josef Bacik <[e-mail]>

---
Changes to v2:
- open-code kunmap() + put_page() (David)
- fix double kunmap() (David)
- don't use bi_set_op_attrs() (David)

Changes to v1:
- move 'super_page' into for-loop in btrfs_scratch_superblocks() (Nikolay)
- switch to using pagecahce instead of alloc_pages() (Nikolay, David)
---
 fs/btrfs/disk-io.c | 89 ++++++++++++++++++++++++++++++----------------
 fs/btrfs/disk-io.h |  4 +--
 fs/btrfs/volumes.c | 66 +++++++++++++++++++++-------------
 fs/btrfs/volumes.h |  2 --
 4 files changed, 102 insertions(+), 59 deletions(-)

Comments

Christoph Hellwig Jan. 28, 2020, 11:47 a.m. UTC | #1

On Tue, Jan 28, 2020 at 12:59:27AM +0900, Johannes Thumshirn wrote:
>  	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
>  	struct btrfs_root *tree_root;
>  	struct btrfs_root *chunk_root;
> +	struct page *super_page;
> +	u8 *superblock;

Any good reason this isn't a struct btrfs_super_block * instead?

> +	csum_type = btrfs_super_csum_type((struct btrfs_super_block *)
> +					  superblock);
>  	if (!btrfs_supported_super_csum(csum_type)) {
>  		btrfs_err(fs_info, "unsupported checksum algorithm: %u",
>  			  csum_type);
>  		err = -EINVAL;
> -		brelse(bh);
> +		kunmap(super_page);
> +		put_page(super_page);
>  		goto fail_alloc;
>  	}
>  
>  	ret = btrfs_init_csum_hash(fs_info, csum_type);
>  	if (ret) {
>  		err = ret;
> +		kunmap(super_page);
> +		put_page(super_page);
>  		goto fail_alloc;
>  	}
>  
> @@ -2861,10 +2867,11 @@ int __cold open_ctree(struct super_block *sb,
>  	 * We want to check superblock checksum, the type is stored inside.
>  	 * Pass the whole disk block of size BTRFS_SUPER_INFO_SIZE (4k).
>  	 */
> -	if (btrfs_check_super_csum(fs_info, bh->b_data)) {
> +	if (btrfs_check_super_csum(fs_info, superblock)) {
>  		btrfs_err(fs_info, "superblock checksum mismatch");
>  		err = -EINVAL;
> -		brelse(bh);
> +		kunmap(super_page);
> +		put_page(super_page);
>  		goto fail_csum;
>  	}
>  
> @@ -2873,8 +2880,9 @@ int __cold open_ctree(struct super_block *sb,
>  	 * following bytes up to INFO_SIZE, the checksum is calculated from
>  	 * the whole block of INFO_SIZE
>  	 */
> -	memcpy(fs_info->super_copy, bh->b_data, sizeof(*fs_info->super_copy));
> -	brelse(bh);
> +	memcpy(fs_info->super_copy, superblock, sizeof(*fs_info->super_copy));
> +	kunmap(super_page);
> +	put_page(super_page);

Would it make sense to move the code up to here in a helper to
simplify the error handling?

>  
>  int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
> -			struct buffer_head **bh_ret)
> +			struct page **super_page)
>  {
> -	struct buffer_head *bh;
>  	struct btrfs_super_block *super;
> +	struct bio_vec bio_vec;
> +	struct bio bio;
> +	struct page *page;
>  	u64 bytenr;
> +	struct address_space *mapping = bdev->bd_inode->i_mapping;
> +	gfp_t gfp_mask;
> +	int ret;
>  
>  	bytenr = btrfs_sb_offset(copy_num);
>  	if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
>  		return -EINVAL;
>  
> -	bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE);
> +	gfp_mask = mapping_gfp_constraint(mapping, ~__GFP_FS) | __GFP_NOFAIL;
> +	page = find_or_create_page(mapping, bytenr >> PAGE_SHIFT, gfp_mask);

Why not simply use read_cache_page_gfp to find or read the page?

> -	super = (struct btrfs_super_block *)bh->b_data;
> +	super = kmap(page);
>  	if (btrfs_super_bytenr(super) != bytenr ||
>  		    btrfs_super_magic(super) != BTRFS_MAGIC) {
> -		brelse(bh);
> +		kunmap(page);
> +		put_page(page);
>  		return -EINVAL;
>  	}
> +	kunmap(page);
>  
> -	*bh_ret = bh;
> +	*super_page = page;

Given that both callers need the kernel virtual address, why not leave it
kmapped?  OTOH if you use read_cache_page_gfp, we could just kill
btrfs_read_dev_one_super and open code the call to read_cache_page_gfp
and btrfs_super_bytenr / btrfs_super_magic in the callers.

> +	bio_init(&bio, &bio_vec, 1);
>  	for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX;
>  		copy_num++) {
> +		u64 bytenr = btrfs_sb_offset(copy_num);
> +		struct page *page;
>  
> -		if (btrfs_read_dev_one_super(bdev, copy_num, &bh))
> +		if (btrfs_read_dev_one_super(bdev, copy_num, &page))
>  			continue;
>  
> -		disk_super = (struct btrfs_super_block *)bh->b_data;
> +		disk_super = kmap(page) + offset_in_page(bytenr);
>  
>  		memset(&disk_super->magic, 0, sizeof(disk_super->magic));
> -		set_buffer_dirty(bh);
> -		sync_dirty_buffer(bh);
> -		brelse(bh);
> +
> +		bio.bi_iter.bi_sector = bytenr >> SECTOR_SHIFT;
> +		bio_set_dev(&bio, bdev);
> +		bio.bi_opf = REQ_OP_WRITE;
> +		bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE,
> +			     offset_in_page(bytenr));
> +
> +		lock_page(page);
> +		submit_bio_wait(&bio);
> +		unlock_page(page);
> +		kunmap(page);
> +		put_page(page);
> +		bio_reset(&bio);

Facoting out the code to write a single sb would clean this up a bit.
Also no real need to keep the page kmapped when under I/O.

Johannes Thumshirn Jan. 30, 2020, 10:12 a.m. UTC | #2

On 28/01/2020 12:47, Christoph Hellwig wrote:
> On Tue, Jan 28, 2020 at 12:59:27AM +0900, Johannes Thumshirn wrote:
>>   	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
>>   	struct btrfs_root *tree_root;
>>   	struct btrfs_root *chunk_root;
>> +	struct page *super_page;
>> +	u8 *superblock;
> 
> Any good reason this isn't a struct btrfs_super_block * instead?

No not really.

[...]

>> @@ -2873,8 +2880,9 @@ int __cold open_ctree(struct super_block *sb,
>>   	 * following bytes up to INFO_SIZE, the checksum is calculated from
>>   	 * the whole block of INFO_SIZE
>>   	 */
>> -	memcpy(fs_info->super_copy, bh->b_data, sizeof(*fs_info->super_copy));
>> -	brelse(bh);
>> +	memcpy(fs_info->super_copy, superblock, sizeof(*fs_info->super_copy));
>> +	kunmap(super_page);
>> +	put_page(super_page);
> 
> Would it make sense to move the code up to here in a helper to
> simplify the error handling?

There is btrfs_release_disk_super() already but David didn't like it's 
use here.

> 
>>   
>>   int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
>> -			struct buffer_head **bh_ret)
>> +			struct page **super_page)
>>   {
>> -	struct buffer_head *bh;
>>   	struct btrfs_super_block *super;
>> +	struct bio_vec bio_vec;
>> +	struct bio bio;
>> +	struct page *page;
>>   	u64 bytenr;
>> +	struct address_space *mapping = bdev->bd_inode->i_mapping;
>> +	gfp_t gfp_mask;
>> +	int ret;
>>   
>>   	bytenr = btrfs_sb_offset(copy_num);
>>   	if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
>>   		return -EINVAL;
>>   
>> -	bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE);
>> +	gfp_mask = mapping_gfp_constraint(mapping, ~__GFP_FS) | __GFP_NOFAIL;
>> +	page = find_or_create_page(mapping, bytenr >> PAGE_SHIFT, gfp_mask);
> 
> Why not simply use read_cache_page_gfp to find or read the page?

right

> 
>> -	super = (struct btrfs_super_block *)bh->b_data;
>> +	super = kmap(page);
>>   	if (btrfs_super_bytenr(super) != bytenr ||
>>   		    btrfs_super_magic(super) != BTRFS_MAGIC) {
>> -		brelse(bh);
>> +		kunmap(page);
>> +		put_page(page);
>>   		return -EINVAL;
>>   	}
>> +	kunmap(page);
>>   
>> -	*bh_ret = bh;
>> +	*super_page = page;
> 
> Given that both callers need the kernel virtual address, why not leave it
> kmapped?  OTOH if you use read_cache_page_gfp, we could just kill
> btrfs_read_dev_one_super and open code the call to read_cache_page_gfp
> and btrfs_super_bytenr / btrfs_super_magic in the callers.

Sounds like a good idea, I'll have a look into it.

> 
>> +	bio_init(&bio, &bio_vec, 1);
>>   	for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX;
>>   		copy_num++) {
>> +		u64 bytenr = btrfs_sb_offset(copy_num);
>> +		struct page *page;
>>   
>> -		if (btrfs_read_dev_one_super(bdev, copy_num, &bh))
>> +		if (btrfs_read_dev_one_super(bdev, copy_num, &page))
>>   			continue;
>>   
>> -		disk_super = (struct btrfs_super_block *)bh->b_data;
>> +		disk_super = kmap(page) + offset_in_page(bytenr);
>>   
>>   		memset(&disk_super->magic, 0, sizeof(disk_super->magic));
>> -		set_buffer_dirty(bh);
>> -		sync_dirty_buffer(bh);
>> -		brelse(bh);
>> +
>> +		bio.bi_iter.bi_sector = bytenr >> SECTOR_SHIFT;
>> +		bio_set_dev(&bio, bdev);
>> +		bio.bi_opf = REQ_OP_WRITE;
>> +		bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE,
>> +			     offset_in_page(bytenr));
>> +
>> +		lock_page(page);
>> +		submit_bio_wait(&bio);
>> +		unlock_page(page);
>> +		kunmap(page);
>> +		put_page(page);
>> +		bio_reset(&bio);
> 
> Facoting out the code to write a single sb would clean this up a bit.
> Also no real need to keep the page kmapped when under I/O.
> 

Yup, will be doing

Patch

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index aea48d6ddc0c..1f30b234ac07 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2635,11 +2635,12 @@  int __cold open_ctree(struct super_block *sb,
 	u64 features;
 	u16 csum_type;
 	struct btrfs_key location;
-	struct buffer_head *bh;
 	struct btrfs_super_block *disk_super;
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
 	struct btrfs_root *tree_root;
 	struct btrfs_root *chunk_root;
+	struct page *super_page;
+	u8 *superblock;
 	int ret;
 	int err = -EINVAL;
 	int clear_free_space_tree = 0;
@@ -2832,28 +2833,33 @@  int __cold open_ctree(struct super_block *sb,
 	/*
 	 * Read super block and check the signature bytes only
 	 */
-	bh = btrfs_read_dev_super(fs_devices->latest_bdev);
-	if (IS_ERR(bh)) {
-		err = PTR_ERR(bh);
+	ret = btrfs_read_dev_super(fs_devices->latest_bdev, &super_page);
+	if (ret) {
+		err = ret;
 		goto fail_alloc;
 	}
 
+	superblock = kmap(super_page);
 	/*
 	 * Verify the type first, if that or the the checksum value are
 	 * corrupted, we'll find out
 	 */
-	csum_type = btrfs_super_csum_type((struct btrfs_super_block *)bh->b_data);
+	csum_type = btrfs_super_csum_type((struct btrfs_super_block *)
+					  superblock);
 	if (!btrfs_supported_super_csum(csum_type)) {
 		btrfs_err(fs_info, "unsupported checksum algorithm: %u",
 			  csum_type);
 		err = -EINVAL;
-		brelse(bh);
+		kunmap(super_page);
+		put_page(super_page);
 		goto fail_alloc;
 	}
 
 	ret = btrfs_init_csum_hash(fs_info, csum_type);
 	if (ret) {
 		err = ret;
+		kunmap(super_page);
+		put_page(super_page);
 		goto fail_alloc;
 	}
 
@@ -2861,10 +2867,11 @@  int __cold open_ctree(struct super_block *sb,
 	 * We want to check superblock checksum, the type is stored inside.
 	 * Pass the whole disk block of size BTRFS_SUPER_INFO_SIZE (4k).
 	 */
-	if (btrfs_check_super_csum(fs_info, bh->b_data)) {
+	if (btrfs_check_super_csum(fs_info, superblock)) {
 		btrfs_err(fs_info, "superblock checksum mismatch");
 		err = -EINVAL;
-		brelse(bh);
+		kunmap(super_page);
+		put_page(super_page);
 		goto fail_csum;
 	}
 
@@ -2873,8 +2880,9 @@  int __cold open_ctree(struct super_block *sb,
 	 * following bytes up to INFO_SIZE, the checksum is calculated from
 	 * the whole block of INFO_SIZE
 	 */
-	memcpy(fs_info->super_copy, bh->b_data, sizeof(*fs_info->super_copy));
-	brelse(bh);
+	memcpy(fs_info->super_copy, superblock, sizeof(*fs_info->super_copy));
+	kunmap(super_page);
+	put_page(super_page);
 
 	disk_super = fs_info->super_copy;
 
@@ -3374,40 +3382,61 @@  static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 }
 
 int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
-			struct buffer_head **bh_ret)
+			struct page **super_page)
 {
-	struct buffer_head *bh;
 	struct btrfs_super_block *super;
+	struct bio_vec bio_vec;
+	struct bio bio;
+	struct page *page;
 	u64 bytenr;
+	struct address_space *mapping = bdev->bd_inode->i_mapping;
+	gfp_t gfp_mask;
+	int ret;
 
 	bytenr = btrfs_sb_offset(copy_num);
 	if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
 		return -EINVAL;
 
-	bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE);
+	gfp_mask = mapping_gfp_constraint(mapping, ~__GFP_FS) | __GFP_NOFAIL;
+	page = find_or_create_page(mapping, bytenr >> PAGE_SHIFT, gfp_mask);
+	if (!page)
+		return -ENOMEM;
+
+	bio_init(&bio, &bio_vec, 1);
+	bio.bi_iter.bi_sector = bytenr >> SECTOR_SHIFT;
+	bio_set_dev(&bio, bdev);
+	bio.bi_opf = REQ_OP_READ;
+	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE,
+		     offset_in_page(bytenr));
+
+	ret = submit_bio_wait(&bio);
+	unlock_page(page);
 	/*
 	 * If we fail to read from the underlying devices, as of now
 	 * the best option we have is to mark it EIO.
 	 */
-	if (!bh)
+	if (ret) {
+		put_page(page);
 		return -EIO;
+	}
 
-	super = (struct btrfs_super_block *)bh->b_data;
+	super = kmap(page);
 	if (btrfs_super_bytenr(super) != bytenr ||
 		    btrfs_super_magic(super) != BTRFS_MAGIC) {
-		brelse(bh);
+		kunmap(page);
+		put_page(page);
 		return -EINVAL;
 	}
+	kunmap(page);
 
-	*bh_ret = bh;
+	*super_page = page;
 	return 0;
 }
 
 
-struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
+int btrfs_read_dev_super(struct block_device *bdev, struct page **page)
 {
-	struct buffer_head *bh;
-	struct buffer_head *latest = NULL;
+	struct page *latest = NULL;
 	struct btrfs_super_block *super;
 	int i;
 	u64 transid = 0;
@@ -3419,25 +3448,25 @@  struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
 	 * later supers, using BTRFS_SUPER_MIRROR_MAX instead
 	 */
 	for (i = 0; i < 1; i++) {
-		ret = btrfs_read_dev_one_super(bdev, i, &bh);
+		ret = btrfs_read_dev_one_super(bdev, i, page);
 		if (ret)
 			continue;
 
-		super = (struct btrfs_super_block *)bh->b_data;
+		super = kmap(*page);
 
 		if (!latest || btrfs_super_generation(super) > transid) {
-			brelse(latest);
-			latest = bh;
+			if (latest) {
+				kunmap(latest);
+				put_page(latest);
+			}
+			latest = *page;
 			transid = btrfs_super_generation(super);
-		} else {
-			brelse(bh);
 		}
-	}
 
-	if (!latest)
-		return ERR_PTR(ret);
+		kunmap(*page);
+	}
 
-	return latest;
+	return ret;
 }
 
 /*
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 8c2d6cf1ce59..e04b233c436a 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -54,9 +54,9 @@  int __cold open_ctree(struct super_block *sb,
 	       char *options);
 void __cold close_ctree(struct btrfs_fs_info *fs_info);
 int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors);
-struct buffer_head *btrfs_read_dev_super(struct block_device *bdev);
+int btrfs_read_dev_super(struct block_device *bdev, struct page **super_page);
 int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
-			struct buffer_head **bh_ret);
+			     struct page **super_page);
 int btrfs_commit_super(struct btrfs_fs_info *fs_info);
 struct btrfs_root *btrfs_read_fs_root(struct btrfs_root *tree_root,
 				      struct btrfs_key *location);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 9cfc668f91f4..fd8b3db14d62 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6,7 +6,6 @@ 
 #include <linux/sched.h>
 #include <linux/bio.h>
 #include <linux/slab.h>
-#include <linux/buffer_head.h>
 #include <linux/blkdev.h>
 #include <linux/ratelimit.h>
 #include <linux/kthread.h>
@@ -500,7 +499,7 @@  static struct btrfs_fs_devices *find_fsid_with_metadata_uuid(
 static int
 btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 		      int flush, struct block_device **bdev,
-		      struct buffer_head **bh)
+		      struct page **super_page)
 {
 	int ret;
 
@@ -519,9 +518,8 @@  btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 		goto error;
 	}
 	invalidate_bdev(*bdev);
-	*bh = btrfs_read_dev_super(*bdev);
-	if (IS_ERR(*bh)) {
-		ret = PTR_ERR(*bh);
+	ret = btrfs_read_dev_super(*bdev, super_page);
+	if (ret) {
 		blkdev_put(*bdev, flags);
 		goto error;
 	}
@@ -530,7 +528,6 @@  btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 
 error:
 	*bdev = NULL;
-	*bh = NULL;
 	return ret;
 }
 
@@ -611,7 +608,7 @@  static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
 {
 	struct request_queue *q;
 	struct block_device *bdev;
-	struct buffer_head *bh;
+	struct page *super_page;
 	struct btrfs_super_block *disk_super;
 	u64 devid;
 	int ret;
@@ -622,17 +619,17 @@  static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
 		return -EINVAL;
 
 	ret = btrfs_get_bdev_and_sb(device->name->str, flags, holder, 1,
-				    &bdev, &bh);
+				    &bdev, &super_page);
 	if (ret)
 		return ret;
 
-	disk_super = (struct btrfs_super_block *)bh->b_data;
+	disk_super = kmap(super_page);
 	devid = btrfs_stack_device_id(&disk_super->dev_item);
 	if (devid != device->devid)
-		goto error_brelse;
+		goto error_free_page;
 
 	if (memcmp(device->uuid, disk_super->dev_item.uuid, BTRFS_UUID_SIZE))
-		goto error_brelse;
+		goto error_free_page;
 
 	device->generation = btrfs_super_generation(disk_super);
 
@@ -641,7 +638,7 @@  static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
 		    BTRFS_FEATURE_INCOMPAT_METADATA_UUID) {
 			pr_err(
 		"BTRFS: Invalid seeding and uuid-changed device detected\n");
-			goto error_brelse;
+			goto error_free_page;
 		}
 
 		clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
@@ -667,12 +664,14 @@  static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
 		fs_devices->rw_devices++;
 		list_add_tail(&device->dev_alloc_list, &fs_devices->alloc_list);
 	}
-	brelse(bh);
+	kunmap(super_page);
+	put_page(super_page);
 
 	return 0;
 
-error_brelse:
-	brelse(bh);
+error_free_page:
+	kunmap(super_page);
+	put_page(super_page);
 	blkdev_put(bdev, flags);
 
 	return -EINVAL;
@@ -2209,14 +2208,15 @@  static struct btrfs_device *btrfs_find_device_by_path(
 	u64 devid;
 	u8 *dev_uuid;
 	struct block_device *bdev;
-	struct buffer_head *bh;
+	struct page *super_page;
 	struct btrfs_device *device;
 
 	ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ,
-				    fs_info->bdev_holder, 0, &bdev, &bh);
+				    fs_info->bdev_holder, 0, &bdev,
+				    &super_page);
 	if (ret)
 		return ERR_PTR(ret);
-	disk_super = (struct btrfs_super_block *)bh->b_data;
+	disk_super = kmap(super_page);
 	devid = btrfs_stack_device_id(&disk_super->dev_item);
 	dev_uuid = disk_super->dev_item.uuid;
 	if (btrfs_fs_incompat(fs_info, METADATA_UUID))
@@ -2226,7 +2226,8 @@  static struct btrfs_device *btrfs_find_device_by_path(
 		device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
 					   disk_super->fsid, true);
 
-	brelse(bh);
+	kunmap(super_page);
+	put_page(super_page);
 	if (!device)
 		device = ERR_PTR(-ENOENT);
 	blkdev_put(bdev, FMODE_READ);
@@ -7319,25 +7320,40 @@  int btrfs_get_dev_stats(struct btrfs_fs_info *fs_info,
 
 void btrfs_scratch_superblocks(struct block_device *bdev, const char *device_path)
 {
-	struct buffer_head *bh;
+	struct bio_vec bio_vec;
+	struct bio bio;
 	struct btrfs_super_block *disk_super;
 	int copy_num;
 
 	if (!bdev)
 		return;
 
+	bio_init(&bio, &bio_vec, 1);
 	for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX;
 		copy_num++) {
+		u64 bytenr = btrfs_sb_offset(copy_num);
+		struct page *page;
 
-		if (btrfs_read_dev_one_super(bdev, copy_num, &bh))
+		if (btrfs_read_dev_one_super(bdev, copy_num, &page))
 			continue;
 
-		disk_super = (struct btrfs_super_block *)bh->b_data;
+		disk_super = kmap(page) + offset_in_page(bytenr);
 
 		memset(&disk_super->magic, 0, sizeof(disk_super->magic));
-		set_buffer_dirty(bh);
-		sync_dirty_buffer(bh);
-		brelse(bh);
+
+		bio.bi_iter.bi_sector = bytenr >> SECTOR_SHIFT;
+		bio_set_dev(&bio, bdev);
+		bio.bi_opf = REQ_OP_WRITE;
+		bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE,
+			     offset_in_page(bytenr));
+
+		lock_page(page);
+		submit_bio_wait(&bio);
+		unlock_page(page);
+		kunmap(page);
+		put_page(page);
+		bio_reset(&bio);
+
 	}
 
 	/* Notify udev that device has changed */
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 690d4f5a0653..3b8eb2a14960 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -17,8 +17,6 @@  extern struct mutex uuid_mutex;
 
 #define BTRFS_STRIPE_LEN	SZ_64K
 
-struct buffer_head;
-
 struct btrfs_io_geometry {
 	/* remaining bytes before crossing a stripe */
 	u64 len;