[PATCH v7 0/8] btrfs: remove buffer heads form superblock handling

[PATCH v7 0/8] btrfs: remove buffer heads form superblock handling

[Johannes Thumshirn]

This patch series removes the use of buffer_heads from btrfs' super block read
and write paths. It also converts the integrity-checking code to only work
with pages and BIOs.

Compared to buffer heads, this gives us a leaner call path, as the
buffer_head code wraps around getting pages from the page-cache and adding
them to BIOs to submit.

Patches one to three are preparatory patches, the first one exports
btrfs_release_disk_super() as a commomn helper to release pages containig a
super block, the second removes the kmap() calls from block device mappings as
suggested by Christoph. The third one unexports btrfs_scratch_superblocks()

The fourth patch removes buffer_heads from superblock reading. The fifth
removes it from super_block writing and the subsequent patches remove the
buffer_heads from the integrity check code.

Due to a rebase error patch #3 of v5 got merged into the patch removing the
BHs form super-block reading, but in the end it isn't too bad this way either.

It's based on misc-next from Monday February 11
(23ba1a90f0571d91b55bdfef7f06f380a74e8475), and doesn't show any regressions
in xfstests to the baseline.

Changes to v6:
- Fixed build warning about unused result of write_one_page() (David)
- Unexport btrfs_scratch_superblocks()

Changes to v5:
- Rebase to newer misc-next
- Merge old patches 2 and 3
- Remove kmap()s of pages from block devices (both in new code as well as
  existing code)

Changes to v4:
- Ressurected Nikolay's patch exporting btrfs_release_disk_super()
- Incroporated feedback from Christoph

Changes to v3:
- Incroporated feedback from Christoph

Changes to v2:
- Removed patch #1 again
- Added Reviews from Josef
- Re-visited page locking, but not changes, it retains the same locking scheme
  the buffer_heads had
- Incroptorated comments from David regarding open-coding functions
- For more details see the idividual patches.

Changes to v1:
- Added patch #1
- Converted sb reading and integrity checking to use the page cache
- Added rationale behind the conversion to the commit messages.
- For more details see the idividual patches.


Johannes Thumshirn (7):
  btrfs: don't kmap() pages from block devices
  btrfs: unexport btrfs_scratch_superblocks
  btrfs: use the page-cache for super block reading
  btrfs: use BIOs instead of buffer_heads from superblock writeout
  btrfs: remove btrfsic_submit_bh()
  btrfs: remove buffer_heads from btrfsic_process_written_block()
  btrfs: remove buffer_heads form superblock mirror integrity checking

Nikolay Borisov (1):
  btrfs: Export btrfs_release_disk_super

 fs/btrfs/check-integrity.c | 215 +++++++++++--------------------------
 fs/btrfs/check-integrity.h |   2 -
 fs/btrfs/disk-io.c         | 191 ++++++++++++++++----------------
 fs/btrfs/disk-io.h         |   6 +-
 fs/btrfs/volumes.c         |  85 ++++++++-------
 fs/btrfs/volumes.h         |   4 +-
 6 files changed, 212 insertions(+), 291 deletions(-)

-- 
2.24.1

[PATCH v7 1/8] btrfs: Export btrfs_release_disk_super

[Johannes Thumshirn]

From: Nikolay Borisov <nborisov@suse.com>

Preparatory patch for removal of buffer_head usage in btrfs.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/volumes.c | 2 +-
 fs/btrfs/volumes.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b092021e41e9..6ebdd95b798d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1247,7 +1247,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	return ret;
 }
 
-static void btrfs_release_disk_super(struct page *page)
+void btrfs_release_disk_super(struct page *page)
 {
 	kunmap(page);
 	put_page(page);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 690d4f5a0653..b7f2edbc6581 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -483,6 +483,7 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset);
 struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
 				       u64 logical, u64 length);
+void btrfs_release_disk_super(struct page *page);
 
 static inline void btrfs_dev_stat_inc(struct btrfs_device *dev,
 				      int index)
-- 
2.24.1

[PATCH v7 2/8] btrfs: don't kmap() pages from block devices

[Johannes Thumshirn]

Block device mappings are never in highmem so kmap() / kunmap() calls for
pages from block devices are unneeded. Use page_address() instead of
kmap() to get to the virtual addreses.

While we're at it, read_cache_page_gfp() doesn't return NULL on error,
only an ERR_PTR, so use IS_ERR() to check for errors.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/volumes.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6ebdd95b798d..620794f1ea64 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1249,7 +1249,6 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 
 void btrfs_release_disk_super(struct page *page)
 {
-	kunmap(page);
 	put_page(page);
 }
 
@@ -1277,10 +1276,10 @@ static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
 	*page = read_cache_page_gfp(bdev->bd_inode->i_mapping,
 				   index, GFP_KERNEL);
 
-	if (IS_ERR_OR_NULL(*page))
+	if (IS_ERR(*page))
 		return 1;
 
-	p = kmap(*page);
+	p = page_address(*page);
 
 	/* align our pointer to the offset of the super block */
 	*disk_super = p + offset_in_page(bytenr);
-- 
2.24.1

[PATCH v7 3/8] btrfs: unexport btrfs_scratch_superblocks

[Johannes Thumshirn]

btrfs_scratch_superblocks() isn't used anywhere outside volumes.c so
remove it from the header file and mark it as static.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/volumes.c | 6 +++++-
 fs/btrfs/volumes.h | 1 -
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 620794f1ea64..e17d4d7a6eb4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -32,6 +32,9 @@
 #include "block-group.h"
 #include "discard.h"
 
+static void btrfs_scratch_superblocks(struct block_device *bdev,
+				      const char *device_path);
+
 const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
 	[BTRFS_RAID_RAID10] = {
 		.sub_stripes	= 2,
@@ -7316,7 +7319,8 @@ int btrfs_get_dev_stats(struct btrfs_fs_info *fs_info,
 	return 0;
 }
 
-void btrfs_scratch_superblocks(struct block_device *bdev, const char *device_path)
+static void btrfs_scratch_superblocks(struct block_device *bdev,
+				      const char *device_path)
 {
 	struct buffer_head *bh;
 	struct btrfs_super_block *disk_super;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index b7f2edbc6581..a3d86ee6a883 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -473,7 +473,6 @@ int btrfs_run_dev_stats(struct btrfs_trans_handle *trans);
 void btrfs_rm_dev_replace_remove_srcdev(struct btrfs_device *srcdev);
 void btrfs_rm_dev_replace_free_srcdev(struct btrfs_device *srcdev);
 void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev);
-void btrfs_scratch_superblocks(struct block_device *bdev, const char *device_path);
 int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info,
 			   u64 logical, u64 len);
 unsigned long btrfs_full_stripe_len(struct btrfs_fs_info *fs_info,
-- 
2.24.1

[PATCH v7 4/8] btrfs: use the page-cache for super block reading

[Johannes Thumshirn]

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.

Directly use the page cache for reading the super-blocks from disk or
invalidating an on-disk super-block. We have to use the page-cache so to
avoid races between mkfs and udev. See also 6f60cbd3ae44 ("btrfs: access
superblock via pagecache in scan_one_device").

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

---
Changes to v6:
- Warn if we can't write out a page for a superblock (David)

Changes to v5:
- Removed kmap()/kunmap() calls (hch/David)

Changes to v4:
- Remove mapping_gfp_constraint() and GFP_NOFAIL (hch)

Changes to v3:
- Use read_cache_pages() and write_one_page() for IO (hch)
- Changed subject (David)
- Dropped Josef's R-b due to change

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 | 74 ++++++++++++++++++------------------------
 fs/btrfs/disk-io.h |  6 ++--
 fs/btrfs/volumes.c | 80 ++++++++++++++++++++++++++--------------------
 fs/btrfs/volumes.h |  4 +--
 4 files changed, 80 insertions(+), 84 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 018681ec159b..9f422edd6cce 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2850,7 +2850,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	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;
@@ -2891,9 +2890,9 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	/*
 	 * 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);
+	disk_super = btrfs_read_dev_super(fs_devices->latest_bdev);
+	if (IS_ERR(disk_super)) {
+		err = PTR_ERR(disk_super);
 		goto fail_alloc;
 	}
 
@@ -2901,18 +2900,19 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	 * 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(disk_super);
 	if (!btrfs_supported_super_csum(csum_type)) {
 		btrfs_err(fs_info, "unsupported checksum algorithm: %u",
 			  csum_type);
 		err = -EINVAL;
-		brelse(bh);
+		btrfs_release_disk_super(disk_super);
 		goto fail_alloc;
 	}
 
 	ret = btrfs_init_csum_hash(fs_info, csum_type);
 	if (ret) {
 		err = ret;
+		btrfs_release_disk_super(disk_super);
 		goto fail_alloc;
 	}
 
@@ -2920,10 +2920,10 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	 * 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, (u8 *) disk_super)) {
 		btrfs_err(fs_info, "superblock checksum mismatch");
 		err = -EINVAL;
-		brelse(bh);
+		btrfs_release_disk_super(disk_super);
 		goto fail_alloc;
 	}
 
@@ -2932,8 +2932,8 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	 * 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, disk_super, sizeof(*fs_info->super_copy));
+	btrfs_release_disk_super(disk_super);
 
 	disk_super = fs_info->super_copy;
 
@@ -3419,45 +3419,38 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 	put_bh(bh);
 }
 
-int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
-			struct buffer_head **bh_ret)
+struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
+						   int copy_num)
 {
-	struct buffer_head *bh;
 	struct btrfs_super_block *super;
+	struct page *page;
 	u64 bytenr;
+	struct address_space *mapping = bdev->bd_inode->i_mapping;
 
 	bytenr = btrfs_sb_offset(copy_num);
 	if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 
-	bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE);
-	/*
-	 * If we fail to read from the underlying devices, as of now
-	 * the best option we have is to mark it EIO.
-	 */
-	if (!bh)
-		return -EIO;
+	page = read_cache_page_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS);
+	if (IS_ERR(page))
+		return ERR_PTR(-ENOMEM);
 
-	super = (struct btrfs_super_block *)bh->b_data;
+	super = page_address(page);
 	if (btrfs_super_bytenr(super) != bytenr ||
 		    btrfs_super_magic(super) != BTRFS_MAGIC) {
-		brelse(bh);
-		return -EINVAL;
+		btrfs_release_disk_super(super);
+		return ERR_PTR(-EINVAL);
 	}
 
-	*bh_ret = bh;
-	return 0;
+	return super;
 }
 
 
-struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
+struct btrfs_super_block *btrfs_read_dev_super(struct block_device *bdev)
 {
-	struct buffer_head *bh;
-	struct buffer_head *latest = NULL;
-	struct btrfs_super_block *super;
+	struct btrfs_super_block *super, *latest = NULL;
 	int i;
 	u64 transid = 0;
-	int ret = -EINVAL;
 
 	/* we would like to check all the supers, but that would make
 	 * a btrfs mount succeed after a mkfs from a different FS.
@@ -3465,25 +3458,20 @@ 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);
-		if (ret)
+		super = btrfs_read_dev_one_super(bdev, i);
+		if (IS_ERR(super))
 			continue;
 
-		super = (struct btrfs_super_block *)bh->b_data;
-
 		if (!latest || btrfs_super_generation(super) > transid) {
-			brelse(latest);
-			latest = bh;
+			if (latest)
+				btrfs_release_disk_super(super);
+
+			latest = super;
 			transid = btrfs_super_generation(super);
-		} else {
-			brelse(bh);
 		}
 	}
 
-	if (!latest)
-		return ERR_PTR(ret);
-
-	return latest;
+	return super;
 }
 
 /*
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index db21ab614357..59c885860bf8 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -56,9 +56,9 @@ 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_one_super(struct block_device *bdev, int copy_num,
-			struct buffer_head **bh_ret);
+struct btrfs_super_block *btrfs_read_dev_super(struct block_device *bdev);
+struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
+						   int copy_num);
 int btrfs_commit_super(struct btrfs_fs_info *fs_info);
 struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
 					struct btrfs_key *key);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e17d4d7a6eb4..daf9c10db337 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>
@@ -32,7 +31,8 @@
 #include "block-group.h"
 #include "discard.h"
 
-static void btrfs_scratch_superblocks(struct block_device *bdev,
+static void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
+				      struct block_device *bdev,
 				      const char *device_path);
 
 const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
@@ -503,7 +503,7 @@ 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 btrfs_super_block **disk_super)
 {
 	int ret;
 
@@ -522,9 +522,9 @@ 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);
+	*disk_super = btrfs_read_dev_super(*bdev);
+	if (IS_ERR(*disk_super)) {
+		ret = PTR_ERR(*disk_super);
 		blkdev_put(*bdev, flags);
 		goto error;
 	}
@@ -533,7 +533,6 @@ btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 
 error:
 	*bdev = NULL;
-	*bh = NULL;
 	return ret;
 }
 
@@ -614,7 +613,6 @@ 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 btrfs_super_block *disk_super;
 	u64 devid;
 	int ret;
@@ -625,17 +623,16 @@ 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, &disk_super);
 	if (ret)
 		return ret;
 
-	disk_super = (struct btrfs_super_block *)bh->b_data;
 	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);
 
@@ -644,7 +641,7 @@ 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);
@@ -670,12 +667,12 @@ 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);
+	btrfs_release_disk_super(disk_super);
 
 	return 0;
 
-error_brelse:
-	brelse(bh);
+error_free_page:
+	btrfs_release_disk_super(disk_super);
 	blkdev_put(bdev, flags);
 
 	return -EINVAL;
@@ -1250,8 +1247,10 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	return ret;
 }
 
-void btrfs_release_disk_super(struct page *page)
+void btrfs_release_disk_super(struct btrfs_super_block *super)
 {
+	struct page *page = virt_to_page(super);
+
 	put_page(page);
 }
 
@@ -1289,7 +1288,7 @@ static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
 
 	if (btrfs_super_bytenr(*disk_super) != bytenr ||
 	    btrfs_super_magic(*disk_super) != BTRFS_MAGIC) {
-		btrfs_release_disk_super(*page);
+		btrfs_release_disk_super(p);
 		return 1;
 	}
 
@@ -1352,7 +1351,7 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, fmode_t flags,
 			btrfs_free_stale_devices(path, device);
 	}
 
-	btrfs_release_disk_super(page);
+	btrfs_release_disk_super(disk_super);
 
 error_bdev_put:
 	blkdev_put(bdev, flags);
@@ -2069,7 +2068,8 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
 	 * supers and free the device.
 	 */
 	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
-		btrfs_scratch_superblocks(device->bdev, device->name->str);
+		btrfs_scratch_superblocks(fs_info, device->bdev,
+					  device->name->str);
 
 	btrfs_close_bdev(device);
 	synchronize_rcu();
@@ -2137,7 +2137,8 @@ void btrfs_rm_dev_replace_free_srcdev(struct btrfs_device *srcdev)
 
 	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &srcdev->dev_state)) {
 		/* zero out the old super if it is writable */
-		btrfs_scratch_superblocks(srcdev->bdev, srcdev->name->str);
+		btrfs_scratch_superblocks(fs_info, srcdev->bdev,
+					  srcdev->name->str);
 	}
 
 	btrfs_close_bdev(srcdev);
@@ -2196,7 +2197,8 @@ void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev)
 	 * is already out of device list, so we don't have to hold
 	 * the device_list_mutex lock.
 	 */
-	btrfs_scratch_superblocks(tgtdev->bdev, tgtdev->name->str);
+	btrfs_scratch_superblocks(tgtdev->fs_info, tgtdev->bdev,
+				  tgtdev->name->str);
 
 	btrfs_close_bdev(tgtdev);
 	synchronize_rcu();
@@ -2211,14 +2213,14 @@ static struct btrfs_device *btrfs_find_device_by_path(
 	u64 devid;
 	u8 *dev_uuid;
 	struct block_device *bdev;
-	struct buffer_head *bh;
 	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,
+				    &disk_super);
 	if (ret)
 		return ERR_PTR(ret);
-	disk_super = (struct btrfs_super_block *)bh->b_data;
+
 	devid = btrfs_stack_device_id(&disk_super->dev_item);
 	dev_uuid = disk_super->dev_item.uuid;
 	if (btrfs_fs_incompat(fs_info, METADATA_UUID))
@@ -2228,7 +2230,7 @@ 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);
+	btrfs_release_disk_super(disk_super);
 	if (!device)
 		device = ERR_PTR(-ENOENT);
 	blkdev_put(bdev, FMODE_READ);
@@ -7319,10 +7321,10 @@ int btrfs_get_dev_stats(struct btrfs_fs_info *fs_info,
 	return 0;
 }
 
-static void btrfs_scratch_superblocks(struct block_device *bdev,
-				      const char *device_path)
+static void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
+			       struct block_device *bdev,
+			       const char *device_path)
 {
-	struct buffer_head *bh;
 	struct btrfs_super_block *disk_super;
 	int copy_num;
 
@@ -7331,16 +7333,24 @@ static void btrfs_scratch_superblocks(struct block_device *bdev,
 
 	for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX;
 		copy_num++) {
+		struct page *page;
+		int err;
 
-		if (btrfs_read_dev_one_super(bdev, copy_num, &bh))
+		disk_super = btrfs_read_dev_one_super(bdev, copy_num);
+		if (IS_ERR(disk_super))
 			continue;
 
-		disk_super = (struct btrfs_super_block *)bh->b_data;
-
 		memset(&disk_super->magic, 0, sizeof(disk_super->magic));
-		set_buffer_dirty(bh);
-		sync_dirty_buffer(bh);
-		brelse(bh);
+
+		page = virt_to_page(disk_super);
+		set_page_dirty(page);
+		lock_page(page); /* write_on_page() unlocks the page */
+		err = write_one_page(page);
+		if (err)
+			btrfs_warn(fs_info, "error clearing superblock number %d (%d)",
+				   copy_num, err);
+		btrfs_release_disk_super(disk_super);
+
 	}
 
 	/* Notify udev that device has changed */
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index a3d86ee6a883..3f52c3a05af8 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;
@@ -482,7 +480,7 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset);
 struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
 				       u64 logical, u64 length);
-void btrfs_release_disk_super(struct page *page);
+void btrfs_release_disk_super(struct btrfs_super_block *super);
 
 static inline void btrfs_dev_stat_inc(struct btrfs_device *dev,
 				      int index)
-- 
2.24.1

[PATCH v7 5/8] btrfs: use BIOs instead of buffer_heads from superblock writeout

[Johannes Thumshirn]

Similar to the superblock read path, change the write path to using BIOs
and pages instead of buffer_heads. This allows us to skip over the
buffer_head code, for writing the superblock to disk.

This is based on a patch originally authored by Nikolay Borisov.

Co-developed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>

---
Changes to v4:
- get rid of op_flags (hch)
- don't use mapping_gfp_constraint() (hch)
- print errno on error (hch)
- use typed pointer (hch)

Changes to v2:
- Don't use bi_set_op_attrs() (David)

Changes to v1:
- Remove left-over buffer_head.h include (David)
---
 fs/btrfs/disk-io.c | 117 ++++++++++++++++++++++++++-------------------
 1 file changed, 67 insertions(+), 50 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9f422edd6cce..906a48f6c996 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -7,7 +7,6 @@
 #include <linux/blkdev.h>
 #include <linux/radix-tree.h>
 #include <linux/writeback.h>
-#include <linux/buffer_head.h>
 #include <linux/workqueue.h>
 #include <linux/kthread.h>
 #include <linux/slab.h>
@@ -3398,25 +3397,34 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 }
 ALLOW_ERROR_INJECTION(open_ctree, ERRNO);
 
-static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
+static void btrfs_end_super_write(struct bio *bio)
 {
-	if (uptodate) {
-		set_buffer_uptodate(bh);
-	} else {
-		struct btrfs_device *device = (struct btrfs_device *)
-			bh->b_private;
-
-		btrfs_warn_rl_in_rcu(device->fs_info,
-				"lost page write due to IO error on %s",
-					  rcu_str_deref(device->name));
-		/* note, we don't set_buffer_write_io_error because we have
-		 * our own ways of dealing with the IO errors
-		 */
-		clear_buffer_uptodate(bh);
-		btrfs_dev_stat_inc_and_print(device, BTRFS_DEV_STAT_WRITE_ERRS);
+	struct btrfs_device *device = bio->bi_private;
+	struct bio_vec *bvec;
+	struct bvec_iter_all iter_all;
+	struct page *page;
+
+	bio_for_each_segment_all(bvec, bio, iter_all) {
+		page = bvec->bv_page;
+
+		if (bio->bi_status) {
+			btrfs_warn_rl_in_rcu(device->fs_info,
+					     "lost page write due to IO error on %s (%d)",
+					     rcu_str_deref(device->name),
+					     blk_status_to_errno(bio->bi_status));
+			ClearPageUptodate(page);
+			SetPageError(page);
+			btrfs_dev_stat_inc_and_print(device,
+						     BTRFS_DEV_STAT_WRITE_ERRS);
+		} else {
+			SetPageUptodate(page);
+		}
+
+		put_page(page);
+		unlock_page(page);
 	}
-	unlock_buffer(bh);
-	put_bh(bh);
+
+	bio_put(bio);
 }
 
 struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
@@ -3482,19 +3490,17 @@ struct btrfs_super_block *btrfs_read_dev_super(struct block_device *bdev)
  * the expected device size at commit time. Note that max_mirrors must be
  * same for write and wait phases.
  *
- * Return number of errors when buffer head is not found or submission fails.
+ * Return number of errors when page is not found or submission fails.
  */
 static int write_dev_supers(struct btrfs_device *device,
 			    struct btrfs_super_block *sb, int max_mirrors)
 {
 	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct address_space *mapping = device->bdev->bd_inode->i_mapping;
 	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
-	struct buffer_head *bh;
 	int i;
-	int ret;
 	int errors = 0;
 	u64 bytenr;
-	int op_flags;
 
 	if (max_mirrors == 0)
 		max_mirrors = BTRFS_SUPER_MIRROR_MAX;
@@ -3502,6 +3508,10 @@ static int write_dev_supers(struct btrfs_device *device,
 	shash->tfm = fs_info->csum_shash;
 
 	for (i = 0; i < max_mirrors; i++) {
+		struct page *page;
+		struct bio *bio;
+		struct btrfs_super_block *disk_super;
+
 		bytenr = btrfs_sb_offset(i);
 		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
 		    device->commit_total_bytes)
@@ -3514,37 +3524,44 @@ static int write_dev_supers(struct btrfs_device *device,
 				    BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
 		crypto_shash_final(shash, sb->csum);
 
-		/* One reference for us, and we leave it for the caller */
-		bh = __getblk(device->bdev, bytenr / BTRFS_BDEV_BLOCKSIZE,
-			      BTRFS_SUPER_INFO_SIZE);
-		if (!bh) {
+		page = find_or_create_page(mapping, bytenr >> PAGE_SHIFT,
+					   GFP_NOFS);
+		if (!page) {
 			btrfs_err(device->fs_info,
-			    "couldn't get super buffer head for bytenr %llu",
+			    "couldn't get superblock page for bytenr %llu",
 			    bytenr);
 			errors++;
 			continue;
 		}
 
-		memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
+		/* Bump the refcount for wait_dev_supers() */
+		get_page(page);
 
-		/* one reference for submit_bh */
-		get_bh(bh);
+		disk_super = page_address(page);
+		memcpy(disk_super, sb, BTRFS_SUPER_INFO_SIZE);
 
-		set_buffer_uptodate(bh);
-		lock_buffer(bh);
-		bh->b_end_io = btrfs_end_buffer_write_sync;
-		bh->b_private = device;
+		/*
+		 * Directly use BIOs here instead of relying on the page-cache
+		 * to do I/O, so we don't loose the ability to do integrity
+		 * checking.
+		 */
+		bio = bio_alloc(GFP_NOFS, 1);
+		bio_set_dev(bio, device->bdev);
+		bio->bi_iter.bi_sector = bytenr >> SECTOR_SHIFT;
+		bio->bi_private = device;
+		bio->bi_end_io = btrfs_end_super_write;
+		__bio_add_page(bio, page, BTRFS_SUPER_INFO_SIZE,
+			       offset_in_page(bytenr));
 
 		/*
-		 * we fua the first super.  The others we allow
+		 * We fua the first super.  The others we allow
 		 * to go down lazy.
 		 */
-		op_flags = REQ_SYNC | REQ_META | REQ_PRIO;
+		bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_META | REQ_PRIO;
 		if (i == 0 && !btrfs_test_opt(device->fs_info, NOBARRIER))
-			op_flags |= REQ_FUA;
-		ret = btrfsic_submit_bh(REQ_OP_WRITE, op_flags, bh);
-		if (ret)
-			errors++;
+			bio->bi_opf |= REQ_FUA;
+
+		btrfsic_submit_bio(bio);
 	}
 	return errors < i ? 0 : -1;
 }
@@ -3553,12 +3570,11 @@ static int write_dev_supers(struct btrfs_device *device,
  * Wait for write completion of superblocks done by write_dev_supers,
  * @max_mirrors same for write and wait phases.
  *
- * Return number of errors when buffer head is not found or not marked up to
+ * Return number of errors when page is not found or not marked up to
  * date.
  */
 static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
 {
-	struct buffer_head *bh;
 	int i;
 	int errors = 0;
 	bool primary_failed = false;
@@ -3568,32 +3584,33 @@ static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
 		max_mirrors = BTRFS_SUPER_MIRROR_MAX;
 
 	for (i = 0; i < max_mirrors; i++) {
+		struct page *page;
+
 		bytenr = btrfs_sb_offset(i);
 		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
 		    device->commit_total_bytes)
 			break;
 
-		bh = __find_get_block(device->bdev,
-				      bytenr / BTRFS_BDEV_BLOCKSIZE,
-				      BTRFS_SUPER_INFO_SIZE);
-		if (!bh) {
+		page = find_get_page(device->bdev->bd_inode->i_mapping,
+				     bytenr >> PAGE_SHIFT);
+		if (!page) {
 			errors++;
 			if (i == 0)
 				primary_failed = true;
 			continue;
 		}
-		wait_on_buffer(bh);
-		if (!buffer_uptodate(bh)) {
+		wait_on_page_locked(page);
+		if (PageError(page)) {
 			errors++;
 			if (i == 0)
 				primary_failed = true;
 		}
 
 		/* drop our reference */
-		brelse(bh);
+		put_page(page);
 
 		/* drop the reference from the writing run */
-		brelse(bh);
+		put_page(page);
 	}
 
 	/* log error, force error return */
-- 
2.24.1

[PATCH v7 6/8] btrfs: remove btrfsic_submit_bh()

[Johannes Thumshirn]

Now that the last use of btrfsic_submit_bh() is gone, remove the function
as well.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/check-integrity.c | 57 --------------------------------------
 fs/btrfs/check-integrity.h |  2 --
 2 files changed, 59 deletions(-)

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index a0ce69f2d27c..e7507985435e 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -2730,63 +2730,6 @@ static struct btrfsic_dev_state *btrfsic_dev_state_lookup(dev_t dev)
 						  &btrfsic_dev_state_hashtable);
 }
 
-int btrfsic_submit_bh(int op, int op_flags, struct buffer_head *bh)
-{
-	struct btrfsic_dev_state *dev_state;
-
-	if (!btrfsic_is_initialized)
-		return submit_bh(op, op_flags, bh);
-
-	mutex_lock(&btrfsic_mutex);
-	/* since btrfsic_submit_bh() might also be called before
-	 * btrfsic_mount(), this might return NULL */
-	dev_state = btrfsic_dev_state_lookup(bh->b_bdev->bd_dev);
-
-	/* Only called to write the superblock (incl. FLUSH/FUA) */
-	if (NULL != dev_state &&
-	    (op == REQ_OP_WRITE) && bh->b_size > 0) {
-		u64 dev_bytenr;
-
-		dev_bytenr = BTRFS_BDEV_BLOCKSIZE * bh->b_blocknr;
-		if (dev_state->state->print_mask &
-		    BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH)
-			pr_info("submit_bh(op=0x%x,0x%x, blocknr=%llu (bytenr %llu), size=%zu, data=%p, bdev=%p)\n",
-			       op, op_flags, (unsigned long long)bh->b_blocknr,
-			       dev_bytenr, bh->b_size, bh->b_data, bh->b_bdev);
-		btrfsic_process_written_block(dev_state, dev_bytenr,
-					      &bh->b_data, 1, NULL,
-					      NULL, bh, op_flags);
-	} else if (NULL != dev_state && (op_flags & REQ_PREFLUSH)) {
-		if (dev_state->state->print_mask &
-		    BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH)
-			pr_info("submit_bh(op=0x%x,0x%x FLUSH, bdev=%p)\n",
-			       op, op_flags, bh->b_bdev);
-		if (!dev_state->dummy_block_for_bio_bh_flush.is_iodone) {
-			if ((dev_state->state->print_mask &
-			     (BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH |
-			      BTRFSIC_PRINT_MASK_VERBOSE)))
-				pr_info("btrfsic_submit_bh(%s) with FLUSH but dummy block already in use (ignored)!\n",
-				       dev_state->name);
-		} else {
-			struct btrfsic_block *const block =
-				&dev_state->dummy_block_for_bio_bh_flush;
-
-			block->is_iodone = 0;
-			block->never_written = 0;
-			block->iodone_w_error = 0;
-			block->flush_gen = dev_state->last_flush_gen + 1;
-			block->submit_bio_bh_rw = op_flags;
-			block->orig_bio_bh_private = bh->b_private;
-			block->orig_bio_bh_end_io.bh = bh->b_end_io;
-			block->next_in_same_bio = NULL;
-			bh->b_private = block;
-			bh->b_end_io = btrfsic_bh_end_io;
-		}
-	}
-	mutex_unlock(&btrfsic_mutex);
-	return submit_bh(op, op_flags, bh);
-}
-
 static void __btrfsic_submit_bio(struct bio *bio)
 {
 	struct btrfsic_dev_state *dev_state;
diff --git a/fs/btrfs/check-integrity.h b/fs/btrfs/check-integrity.h
index 9bf4359cc44c..bcc730a06cb5 100644
--- a/fs/btrfs/check-integrity.h
+++ b/fs/btrfs/check-integrity.h
@@ -7,11 +7,9 @@
 #define BTRFS_CHECK_INTEGRITY_H
 
 #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
-int btrfsic_submit_bh(int op, int op_flags, struct buffer_head *bh);
 void btrfsic_submit_bio(struct bio *bio);
 int btrfsic_submit_bio_wait(struct bio *bio);
 #else
-#define btrfsic_submit_bh submit_bh
 #define btrfsic_submit_bio submit_bio
 #define btrfsic_submit_bio_wait submit_bio_wait
 #endif
-- 
2.24.1

[PATCH v7 7/8] btrfs: remove buffer_heads from btrfsic_process_written_block()

[Johannes Thumshirn]

Now that the last caller of btrfsic_process_written_block() with
buffer_heads is gone, remove the buffer_head processing path from it as
well.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/check-integrity.c | 103 +++++++++----------------------------
 1 file changed, 25 insertions(+), 78 deletions(-)

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index e7507985435e..4f6db2fe482a 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -152,11 +152,8 @@ struct btrfsic_block {
 	struct list_head ref_to_list;	/* list */
 	struct list_head ref_from_list;	/* list */
 	struct btrfsic_block *next_in_same_bio;
-	void *orig_bio_bh_private;
-	union {
-		bio_end_io_t *bio;
-		bh_end_io_t *bh;
-	} orig_bio_bh_end_io;
+	void *orig_bio_private;
+	bio_end_io_t *orig_bio_end_io;
 	int submit_bio_bh_rw;
 	u64 flush_gen; /* only valid if !never_written */
 };
@@ -325,14 +322,12 @@ static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
 					  u64 dev_bytenr, char **mapped_datav,
 					  unsigned int num_pages,
 					  struct bio *bio, int *bio_is_patched,
-					  struct buffer_head *bh,
 					  int submit_bio_bh_rw);
 static int btrfsic_process_written_superblock(
 		struct btrfsic_state *state,
 		struct btrfsic_block *const block,
 		struct btrfs_super_block *const super_hdr);
 static void btrfsic_bio_end_io(struct bio *bp);
-static void btrfsic_bh_end_io(struct buffer_head *bh, int uptodate);
 static int btrfsic_is_block_ref_by_superblock(const struct btrfsic_state *state,
 					      const struct btrfsic_block *block,
 					      int recursion_level);
@@ -399,8 +394,8 @@ static void btrfsic_block_init(struct btrfsic_block *b)
 	b->never_written = 0;
 	b->mirror_num = 0;
 	b->next_in_same_bio = NULL;
-	b->orig_bio_bh_private = NULL;
-	b->orig_bio_bh_end_io.bio = NULL;
+	b->orig_bio_private = NULL;
+	b->orig_bio_end_io = NULL;
 	INIT_LIST_HEAD(&b->collision_resolving_node);
 	INIT_LIST_HEAD(&b->all_blocks_node);
 	INIT_LIST_HEAD(&b->ref_to_list);
@@ -1743,7 +1738,6 @@ static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
 					  u64 dev_bytenr, char **mapped_datav,
 					  unsigned int num_pages,
 					  struct bio *bio, int *bio_is_patched,
-					  struct buffer_head *bh,
 					  int submit_bio_bh_rw)
 {
 	int is_metadata;
@@ -1902,9 +1896,9 @@ static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
 				block->is_iodone = 0;
 				BUG_ON(NULL == bio_is_patched);
 				if (!*bio_is_patched) {
-					block->orig_bio_bh_private =
+					block->orig_bio_private =
 					    bio->bi_private;
-					block->orig_bio_bh_end_io.bio =
+					block->orig_bio_end_io =
 					    bio->bi_end_io;
 					block->next_in_same_bio = NULL;
 					bio->bi_private = block;
@@ -1916,25 +1910,17 @@ static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
 					    bio->bi_private;
 
 					BUG_ON(NULL == chained_block);
-					block->orig_bio_bh_private =
-					    chained_block->orig_bio_bh_private;
-					block->orig_bio_bh_end_io.bio =
-					    chained_block->orig_bio_bh_end_io.
-					    bio;
+					block->orig_bio_private =
+					    chained_block->orig_bio_private;
+					block->orig_bio_end_io =
+					    chained_block->orig_bio_end_io;
 					block->next_in_same_bio = chained_block;
 					bio->bi_private = block;
 				}
-			} else if (NULL != bh) {
-				block->is_iodone = 0;
-				block->orig_bio_bh_private = bh->b_private;
-				block->orig_bio_bh_end_io.bh = bh->b_end_io;
-				block->next_in_same_bio = NULL;
-				bh->b_private = block;
-				bh->b_end_io = btrfsic_bh_end_io;
 			} else {
 				block->is_iodone = 1;
-				block->orig_bio_bh_private = NULL;
-				block->orig_bio_bh_end_io.bio = NULL;
+				block->orig_bio_private = NULL;
+				block->orig_bio_end_io = NULL;
 				block->next_in_same_bio = NULL;
 			}
 		}
@@ -2042,8 +2028,8 @@ static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
 			block->is_iodone = 0;
 			BUG_ON(NULL == bio_is_patched);
 			if (!*bio_is_patched) {
-				block->orig_bio_bh_private = bio->bi_private;
-				block->orig_bio_bh_end_io.bio = bio->bi_end_io;
+				block->orig_bio_private = bio->bi_private;
+				block->orig_bio_end_io = bio->bi_end_io;
 				block->next_in_same_bio = NULL;
 				bio->bi_private = block;
 				bio->bi_end_io = btrfsic_bio_end_io;
@@ -2054,24 +2040,17 @@ static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
 				    bio->bi_private;
 
 				BUG_ON(NULL == chained_block);
-				block->orig_bio_bh_private =
-				    chained_block->orig_bio_bh_private;
-				block->orig_bio_bh_end_io.bio =
-				    chained_block->orig_bio_bh_end_io.bio;
+				block->orig_bio_private =
+				    chained_block->orig_bio_private;
+				block->orig_bio_end_io =
+				    chained_block->orig_bio_end_io;
 				block->next_in_same_bio = chained_block;
 				bio->bi_private = block;
 			}
-		} else if (NULL != bh) {
-			block->is_iodone = 0;
-			block->orig_bio_bh_private = bh->b_private;
-			block->orig_bio_bh_end_io.bh = bh->b_end_io;
-			block->next_in_same_bio = NULL;
-			bh->b_private = block;
-			bh->b_end_io = btrfsic_bh_end_io;
 		} else {
 			block->is_iodone = 1;
-			block->orig_bio_bh_private = NULL;
-			block->orig_bio_bh_end_io.bio = NULL;
+			block->orig_bio_private = NULL;
+			block->orig_bio_end_io = NULL;
 			block->next_in_same_bio = NULL;
 		}
 		if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
@@ -2112,8 +2091,8 @@ static void btrfsic_bio_end_io(struct bio *bp)
 		iodone_w_error = 1;
 
 	BUG_ON(NULL == block);
-	bp->bi_private = block->orig_bio_bh_private;
-	bp->bi_end_io = block->orig_bio_bh_end_io.bio;
+	bp->bi_private = block->orig_bio_private;
+	bp->bi_end_io = block->orig_bio_end_io;
 
 	do {
 		struct btrfsic_block *next_block;
@@ -2146,38 +2125,6 @@ static void btrfsic_bio_end_io(struct bio *bp)
 	bp->bi_end_io(bp);
 }
 
-static void btrfsic_bh_end_io(struct buffer_head *bh, int uptodate)
-{
-	struct btrfsic_block *block = (struct btrfsic_block *)bh->b_private;
-	int iodone_w_error = !uptodate;
-	struct btrfsic_dev_state *dev_state;
-
-	BUG_ON(NULL == block);
-	dev_state = block->dev_state;
-	if ((dev_state->state->print_mask & BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
-		pr_info("bh_end_io(error=%d) for %c @%llu (%s/%llu/%d)\n",
-		       iodone_w_error,
-		       btrfsic_get_block_type(dev_state->state, block),
-		       block->logical_bytenr, block->dev_state->name,
-		       block->dev_bytenr, block->mirror_num);
-
-	block->iodone_w_error = iodone_w_error;
-	if (block->submit_bio_bh_rw & REQ_PREFLUSH) {
-		dev_state->last_flush_gen++;
-		if ((dev_state->state->print_mask &
-		     BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
-			pr_info("bh_end_io() new %s flush_gen=%llu\n",
-			       dev_state->name, dev_state->last_flush_gen);
-	}
-	if (block->submit_bio_bh_rw & REQ_FUA)
-		block->flush_gen = 0; /* FUA completed means block is on disk */
-
-	bh->b_private = block->orig_bio_bh_private;
-	bh->b_end_io = block->orig_bio_bh_end_io.bh;
-	block->is_iodone = 1; /* for FLUSH, this releases the block */
-	bh->b_end_io(bh, uptodate);
-}
-
 static int btrfsic_process_written_superblock(
 		struct btrfsic_state *state,
 		struct btrfsic_block *const superblock,
@@ -2781,7 +2728,7 @@ static void __btrfsic_submit_bio(struct bio *bio)
 		btrfsic_process_written_block(dev_state, dev_bytenr,
 					      mapped_datav, segs,
 					      bio, &bio_is_patched,
-					      NULL, bio->bi_opf);
+					      bio->bi_opf);
 		bio_for_each_segment(bvec, bio, iter)
 			kunmap(bvec.bv_page);
 		kfree(mapped_datav);
@@ -2805,8 +2752,8 @@ static void __btrfsic_submit_bio(struct bio *bio)
 			block->iodone_w_error = 0;
 			block->flush_gen = dev_state->last_flush_gen + 1;
 			block->submit_bio_bh_rw = bio->bi_opf;
-			block->orig_bio_bh_private = bio->bi_private;
-			block->orig_bio_bh_end_io.bio = bio->bi_end_io;
+			block->orig_bio_private = bio->bi_private;
+			block->orig_bio_end_io = bio->bi_end_io;
 			block->next_in_same_bio = NULL;
 			bio->bi_private = block;
 			bio->bi_end_io = btrfsic_bio_end_io;
-- 
2.24.1

[PATCH v7 8/8] btrfs: remove buffer_heads form superblock mirror integrity checking

[Johannes Thumshirn]

The integrity checking code for the superblock mirrors is the last remaining
user of buffer_heads in BTRFS, change it to using plain BIOs as well.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>

---
Changes to v4:
- Remove mapping_gfp_constraint()

Changes to v2:
- Open-code kunmap() + put_page() (David)
- Remove __GFP_NOFAIL from allocation (Josef)
- Merge error paths (David)

Changes to v1:
- Convert from alloc_page() to find_or_create_page()
---
 fs/btrfs/check-integrity.c | 55 +++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 4f6db2fe482a..e10a27d6db08 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -77,7 +77,6 @@
 
 #include <linux/sched.h>
 #include <linux/slab.h>
-#include <linux/buffer_head.h>
 #include <linux/mutex.h>
 #include <linux/genhd.h>
 #include <linux/blkdev.h>
@@ -762,29 +761,45 @@ static int btrfsic_process_superblock_dev_mirror(
 	struct btrfs_fs_info *fs_info = state->fs_info;
 	struct btrfs_super_block *super_tmp;
 	u64 dev_bytenr;
-	struct buffer_head *bh;
 	struct btrfsic_block *superblock_tmp;
 	int pass;
 	struct block_device *const superblock_bdev = device->bdev;
+	struct page *page;
+	struct bio bio;
+	struct bio_vec bio_vec;
+	struct address_space *mapping = superblock_bdev->bd_inode->i_mapping;
+	int ret;
 
 	/* super block bytenr is always the unmapped device bytenr */
 	dev_bytenr = btrfs_sb_offset(superblock_mirror_num);
 	if (dev_bytenr + BTRFS_SUPER_INFO_SIZE > device->commit_total_bytes)
 		return -1;
-	bh = __bread(superblock_bdev, dev_bytenr / BTRFS_BDEV_BLOCKSIZE,
-		     BTRFS_SUPER_INFO_SIZE);
-	if (NULL == bh)
+
+	page = find_or_create_page(mapping, dev_bytenr >> PAGE_SHIFT, GFP_NOFS);
+	if (!page)
+		return -1;
+
+	bio_init(&bio, &bio_vec, 1);
+	bio.bi_iter.bi_sector = dev_bytenr >> SECTOR_SHIFT;
+	bio_set_dev(&bio, superblock_bdev);
+	bio_set_op_attrs(&bio, REQ_OP_READ, 0);
+	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
+
+	ret = submit_bio_wait(&bio);
+	if (ret)
 		return -1;
-	super_tmp = (struct btrfs_super_block *)
-	    (bh->b_data + (dev_bytenr & (BTRFS_BDEV_BLOCKSIZE - 1)));
+
+	unlock_page(page);
+
+	super_tmp = kmap(page);
 
 	if (btrfs_super_bytenr(super_tmp) != dev_bytenr ||
 	    btrfs_super_magic(super_tmp) != BTRFS_MAGIC ||
 	    memcmp(device->uuid, super_tmp->dev_item.uuid, BTRFS_UUID_SIZE) ||
 	    btrfs_super_nodesize(super_tmp) != state->metablock_size ||
 	    btrfs_super_sectorsize(super_tmp) != state->datablock_size) {
-		brelse(bh);
-		return 0;
+		ret = 0;
+		goto out_unmap;
 	}
 
 	superblock_tmp =
@@ -795,8 +810,8 @@ static int btrfsic_process_superblock_dev_mirror(
 		superblock_tmp = btrfsic_block_alloc();
 		if (NULL == superblock_tmp) {
 			pr_info("btrfsic: error, kmalloc failed!\n");
-			brelse(bh);
-			return -1;
+			ret = -1;
+			goto out_unmap;
 		}
 		/* for superblock, only the dev_bytenr makes sense */
 		superblock_tmp->dev_bytenr = dev_bytenr;
@@ -880,8 +895,8 @@ static int btrfsic_process_superblock_dev_mirror(
 					      mirror_num)) {
 				pr_info("btrfsic: btrfsic_map_block(bytenr @%llu, mirror %d) failed!\n",
 				       next_bytenr, mirror_num);
-				brelse(bh);
-				return -1;
+				ret = -1;
+				goto out_unmap;
 			}
 
 			next_block = btrfsic_block_lookup_or_add(
@@ -890,8 +905,8 @@ static int btrfsic_process_superblock_dev_mirror(
 					mirror_num, NULL);
 			if (NULL == next_block) {
 				btrfsic_release_block_ctx(&tmp_next_block_ctx);
-				brelse(bh);
-				return -1;
+				ret = -1;
+				goto out_unmap;
 			}
 
 			next_block->disk_key = tmp_disk_key;
@@ -902,16 +917,18 @@ static int btrfsic_process_superblock_dev_mirror(
 					BTRFSIC_GENERATION_UNKNOWN);
 			btrfsic_release_block_ctx(&tmp_next_block_ctx);
 			if (NULL == l) {
-				brelse(bh);
-				return -1;
+				ret = -1;
+				goto out_unmap;
 			}
 		}
 	}
 	if (state->print_mask & BTRFSIC_PRINT_MASK_INITIAL_ALL_TREES)
 		btrfsic_dump_tree_sub(state, superblock_tmp, 0);
 
-	brelse(bh);
-	return 0;
+out_unmap:
+	kunmap(page);
+	put_page(page);
+	return ret;
 }
 
 static struct btrfsic_stack_frame *btrfsic_stack_frame_alloc(void)
-- 
2.24.1

Re: [PATCH v7 2/8] btrfs: don't kmap() pages from block devices

[Christoph Hellwig]

On Wed, Feb 12, 2020 at 04:16:58PM +0900, Johannes Thumshirn wrote:
> Block device mappings are never in highmem so kmap() / kunmap() calls for
> pages from block devices are unneeded. Use page_address() instead of
> kmap() to get to the virtual addreses.
> 
> While we're at it, read_cache_page_gfp() doesn't return NULL on error,
> only an ERR_PTR, so use IS_ERR() to check for errors.
> 
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Looks good,

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

Re: [PATCH v7 3/8] btrfs: unexport btrfs_scratch_superblocks

[Christoph Hellwig]

On Wed, Feb 12, 2020 at 04:16:59PM +0900, Johannes Thumshirn wrote:
> btrfs_scratch_superblocks() isn't used anywhere outside volumes.c so
> remove it from the header file and mark it as static.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

It wasn't exported to start with, just global scope while you
mark it static now.

Re: [PATCH v7 4/8] btrfs: use the page-cache for super block reading

[Christoph Hellwig]

On Wed, Feb 12, 2020 at 04:17:00PM +0900, Johannes Thumshirn wrote:
> 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.
> 
> Directly use the page cache for reading the super-blocks from disk or
> invalidating an on-disk super-block. We have to use the page-cache so to
> avoid races between mkfs and udev. See also 6f60cbd3ae44 ("btrfs: access
> superblock via pagecache in scan_one_device").
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> 
> ---
> Changes to v6:
> - Warn if we can't write out a page for a superblock (David)

Shouldn't there be some real error handling instead of just a warning?
At least shut down the file system?

Re: [PATCH v7 5/8] btrfs: use BIOs instead of buffer_heads from superblock writeout

[Christoph Hellwig]

Looks good,

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

Re: [PATCH v7 4/8] btrfs: use the page-cache for super block reading

[Johannes Thumshirn]

On 12/02/2020 08:28, Christoph Hellwig wrote:
>> - Warn if we can't write out a page for a superblock (David)
> 
> Shouldn't there be some real error handling instead of just a warning?
> At least shut down the file system?

Looking at the callers of btrfs_scratch_superblock() I don't think so. 
btrfs_scratch_superblock() is called by btrfs_rm_device(), 
btrfs_rm_dev_replace_free_srcdev() and 
btrfs_destroy_dev_replace_tgtdev(). So it's all functions related to 
removing a device from a multi device file-system. Do you really want to 
shut down the file-system if clearing the magic in one of the 
super-blocks of a disk that is to be removed from the file-system 
doesn't work?

I think it's better to warn the administrator that something didn't work 
all to well and to be cautious with that disk if he/she ever want's to 
put it back than shut down the whole FS.

Thanks,
	Johannes

Re: [PATCH v7 3/8] btrfs: unexport btrfs_scratch_superblocks

[Johannes Thumshirn]

On 12/02/2020 08:27, Christoph Hellwig wrote:
> On Wed, Feb 12, 2020 at 04:16:59PM +0900, Johannes Thumshirn wrote:
>> btrfs_scratch_superblocks() isn't used anywhere outside volumes.c so
>> remove it from the header file and mark it as static.
>>
>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> 
> It wasn't exported to start with, just global scope while you
> mark it static now.
> 

I think David can tweak the commit message when applying.

Re: [PATCH v7 8/8] btrfs: remove buffer_heads form superblock mirror integrity checking

[David Sterba]

On Wed, Feb 12, 2020 at 04:17:04PM +0900, Johannes Thumshirn wrote:
> @@ -762,29 +761,45 @@ static int btrfsic_process_superblock_dev_mirror(
>  	struct btrfs_fs_info *fs_info = state->fs_info;
>  	struct btrfs_super_block *super_tmp;
>  	u64 dev_bytenr;
> -	struct buffer_head *bh;
>  	struct btrfsic_block *superblock_tmp;
>  	int pass;
>  	struct block_device *const superblock_bdev = device->bdev;
> +	struct page *page;
> +	struct bio bio;
> +	struct bio_vec bio_vec;
> +	struct address_space *mapping = superblock_bdev->bd_inode->i_mapping;
> +	int ret;
>  
>  	/* super block bytenr is always the unmapped device bytenr */
>  	dev_bytenr = btrfs_sb_offset(superblock_mirror_num);
>  	if (dev_bytenr + BTRFS_SUPER_INFO_SIZE > device->commit_total_bytes)
>  		return -1;
> -	bh = __bread(superblock_bdev, dev_bytenr / BTRFS_BDEV_BLOCKSIZE,
> -		     BTRFS_SUPER_INFO_SIZE);
> -	if (NULL == bh)
> +
> +	page = find_or_create_page(mapping, dev_bytenr >> PAGE_SHIFT, GFP_NOFS);
> +	if (!page)
> +		return -1;
> +
> +	bio_init(&bio, &bio_vec, 1);
> +	bio.bi_iter.bi_sector = dev_bytenr >> SECTOR_SHIFT;
> +	bio_set_dev(&bio, superblock_bdev);
> +	bio_set_op_attrs(&bio, REQ_OP_READ, 0);
> +	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
> +
> +	ret = submit_bio_wait(&bio);
> +	if (ret)
>  		return -1;
> -	super_tmp = (struct btrfs_super_block *)
> -	    (bh->b_data + (dev_bytenr & (BTRFS_BDEV_BLOCKSIZE - 1)));
> +
> +	unlock_page(page);
> +
> +	super_tmp = kmap(page);

I beleve the same reasoning applies here regarding kmap, it's the bdev
mapping and we won't get a highmem page.

>  
>  	if (btrfs_super_bytenr(super_tmp) != dev_bytenr ||
>  	    btrfs_super_magic(super_tmp) != BTRFS_MAGIC ||
>  	    memcmp(device->uuid, super_tmp->dev_item.uuid, BTRFS_UUID_SIZE) ||
>  	    btrfs_super_nodesize(super_tmp) != state->metablock_size ||
>  	    btrfs_super_sectorsize(super_tmp) != state->datablock_size) {
> -		brelse(bh);
> -		return 0;
> +		ret = 0;
> +		goto out_unmap;
>  	}
>  
>  	superblock_tmp =

Re: [PATCH v7 8/8] btrfs: remove buffer_heads form superblock mirror integrity checking

[Johannes Thumshirn]

On 12/02/2020 18:06, David Sterba wrote:
> On Wed, Feb 12, 2020 at 04:17:04PM +0900, Johannes Thumshirn wrote:
>> @@ -762,29 +761,45 @@ static int btrfsic_process_superblock_dev_mirror(
>>   	struct btrfs_fs_info *fs_info = state->fs_info;
>>   	struct btrfs_super_block *super_tmp;
>>   	u64 dev_bytenr;
>> -	struct buffer_head *bh;
>>   	struct btrfsic_block *superblock_tmp;
>>   	int pass;
>>   	struct block_device *const superblock_bdev = device->bdev;
>> +	struct page *page;
>> +	struct bio bio;
>> +	struct bio_vec bio_vec;
>> +	struct address_space *mapping = superblock_bdev->bd_inode->i_mapping;
>> +	int ret;
>>   
>>   	/* super block bytenr is always the unmapped device bytenr */
>>   	dev_bytenr = btrfs_sb_offset(superblock_mirror_num);
>>   	if (dev_bytenr + BTRFS_SUPER_INFO_SIZE > device->commit_total_bytes)
>>   		return -1;
>> -	bh = __bread(superblock_bdev, dev_bytenr / BTRFS_BDEV_BLOCKSIZE,
>> -		     BTRFS_SUPER_INFO_SIZE);
>> -	if (NULL == bh)
>> +
>> +	page = find_or_create_page(mapping, dev_bytenr >> PAGE_SHIFT, GFP_NOFS);
>> +	if (!page)
>> +		return -1;
>> +
>> +	bio_init(&bio, &bio_vec, 1);
>> +	bio.bi_iter.bi_sector = dev_bytenr >> SECTOR_SHIFT;
>> +	bio_set_dev(&bio, superblock_bdev);
>> +	bio_set_op_attrs(&bio, REQ_OP_READ, 0);
>> +	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
>> +
>> +	ret = submit_bio_wait(&bio);
>> +	if (ret)
>>   		return -1;
>> -	super_tmp = (struct btrfs_super_block *)
>> -	    (bh->b_data + (dev_bytenr & (BTRFS_BDEV_BLOCKSIZE - 1)));
>> +
>> +	unlock_page(page);
>> +
>> +	super_tmp = kmap(page);
> 
> I beleve the same reasoning applies here regarding kmap, it's the bdev
> mapping and we won't get a highmem page.
> 

Ah damn it my bad and __bio_add_page() as well. Can I send you a 
follow-on patch to fold in?