On 14.03.2018 22:11, fdman...@kernel.org wrote:
> From: Filipe Manana <fdman...@suse.com>
>
> Under some cases the filesystem checker reports an error when it finds
> checksum items for an extent that is referenced by an inode as a prealloc
> extent. Such cases are not an error when the extent is actually shared
> (was cloned/reflinked) with other inodes and was written through one of
> those other inodes.
>
> Example:
>
> $ mkfs.btrfs -f /dev/sdb
> $ mount /dev/sdb /mnt
>
> $ touch /mnt/foo
> $ xfs_io -c "falloc 0 256K" /mnt/foo
> $ sync
>
> $ xfs_io -c "pwrite -S 0xab 0 256K" /mnt/foo
> $ touch /mnt/bar
> $ xfs_io -c "reflink /mnt/foo 0 0 256K" /mnt/bar
> $ xfs_io -c "fsync" /mnt/bar
>
> <power fail>
> $ mount /dev/sdb /mnt
> $ umount /mnt
>
> $ btrfs check /dev/sdc
> Checking filesystem on /dev/sdb
> UUID: 52d3006e-ee3b-40eb-aa21-e56253a03d39
> checking extents
> checking free space cache
> checking fs roots
> root 5 inode 257 errors 800, odd csum item
> ERROR: errors found in fs roots
> found 688128 bytes used, error(s) found
> total csum bytes: 256
> total tree bytes: 163840
> total fs tree bytes: 65536
> total extent tree bytes: 16384
> btree space waste bytes: 138819
> file data blocks allocated: 10747904
> referenced 10747904
> $ echo $?
> 1
>
> So teach check to not report such cases as errors by checking if the
> extent is shared with other inodes and if so, consider it an error the
> existence of checksum items only if all those other inodes are referencing
> the extent as a prealloc extent.
> This case can be hit often when running the generic/475 testcase from
> fstests.
>
> A test case will follow in a separate patch.
>
> Signed-off-by: Filipe Manana <fdman...@suse.com>
Reviewed-by: Nikolay Borisov <nbori...@suse.com>
> ---
>
> V3: Replaced incorrect argument to a btrfs_next_leaf() call (extent_root ->
> root).
>
> V2: Made stuff work with lowmem mode as well.
> Added a comment about the limitations of the current check.
> Removed filtering by inode number since it was unreliable as we can
> have different inodes with same inode number but in different roots
> (so opted to drop the filtering instead of filtering by root as well,
> to keep it simpler).
>
>
> check/main.c | 11 ++-
> check/mode-common.c | 258
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> check/mode-common.h | 3 +
> check/mode-lowmem.c | 14 ++-
> 4 files changed, 281 insertions(+), 5 deletions(-)
>
> diff --git a/check/main.c b/check/main.c
> index 392195ca..88e6c1e9 100644
> --- a/check/main.c
> +++ b/check/main.c
> @@ -1515,8 +1515,15 @@ static int process_file_extent(struct btrfs_root *root,
> if (found < num_bytes)
> rec->some_csum_missing = 1;
> } else if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
> - if (found > 0)
> - rec->errors |= I_ERR_ODD_CSUM_ITEM;
> + if (found > 0) {
> + ret =
> check_prealloc_extent_written(root->fs_info,
> + disk_bytenr,
> + num_bytes);
> + if (ret < 0)
> + return ret;
> + if (ret == 0)
> + rec->errors |= I_ERR_ODD_CSUM_ITEM;
> + }
> }
> }
> return 0;
> diff --git a/check/mode-common.c b/check/mode-common.c
> index 1b56a968..8a59e8a4 100644
> --- a/check/mode-common.c
> +++ b/check/mode-common.c
> @@ -24,6 +24,264 @@
> #include "check/mode-common.h"
>
> /*
> + * Check if the inode referenced by the given data reference uses the extent
> + * at disk_bytenr as a non-prealloc extent.
> + *
> + * Returns 1 if true, 0 if false and < 0 on error.
> + */
> +static int check_prealloc_data_ref(struct btrfs_fs_info *fs_info,
> + u64 disk_bytenr,
> + struct btrfs_extent_data_ref *dref,
> + struct extent_buffer *eb)
> +{
> + u64 rootid = btrfs_extent_data_ref_root(eb, dref);
> + u64 objectid = btrfs_extent_data_ref_objectid(eb, dref);
> + u64 offset = btrfs_extent_data_ref_offset(eb, dref);
> + struct btrfs_root *root;
> + struct btrfs_key key;
> + struct btrfs_path path;
> + int ret;
> +
> + btrfs_init_path(&path);
> + key.objectid = rootid;
> + key.type = BTRFS_ROOT_ITEM_KEY;
> + key.offset = (u64)-1;
> + root = btrfs_read_fs_root(fs_info, &key);
> + if (IS_ERR(root)) {
> + ret = PTR_ERR(root);
> + goto out;
> + }
> +
> + key.objectid = objectid;
> + key.type = BTRFS_EXTENT_DATA_KEY;
> + key.offset = offset;
> + ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
> + if (ret > 0) {
> + fprintf(stderr,
> + "Missing file extent item for inode %llu, root %llu,
> offset %llu",
> + objectid, rootid, offset);
> + ret = -ENOENT;
> + }
> + if (ret < 0)
> + goto out;
> +
> + while (true) {
> + struct btrfs_file_extent_item *fi;
> + int extent_type;
> +
> + if (path.slots[0] >= btrfs_header_nritems(path.nodes[0])) {
> + ret = btrfs_next_leaf(root, &path);
> + if (ret < 0)
> + goto out;
> + if (ret > 0)
> + break;
> + }
> +
> + btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);
> + if (key.objectid != objectid ||
> + key.type != BTRFS_EXTENT_DATA_KEY)
> + break;
> +
> + fi = btrfs_item_ptr(path.nodes[0], path.slots[0],
> + struct btrfs_file_extent_item);
> + extent_type = btrfs_file_extent_type(path.nodes[0], fi);
> + if (extent_type != BTRFS_FILE_EXTENT_REG &&
> + extent_type != BTRFS_FILE_EXTENT_PREALLOC)
> + goto next;
> +
> + if (btrfs_file_extent_disk_bytenr(path.nodes[0], fi) !=
> + disk_bytenr)
> + break;
> +
> + if (extent_type == BTRFS_FILE_EXTENT_REG) {
> + ret = 1;
> + goto out;
> + }
> +next:
> + path.slots[0]++;
> + }
> + ret = 0;
> + out:
> + btrfs_release_path(&path);
> + return ret;
> +}
> +
> +/*
> + * Check if a shared data reference points to a node that has a file extent
> item
> + * pointing to the extent at @disk_bytenr that is not of type prealloc.
> + *
> + * Returns 1 if true, 0 if false and < 0 on error.
> + */
> +static int check_prealloc_shared_data_ref(struct btrfs_fs_info *fs_info,
> + u64 parent,
> + u64 disk_bytenr)
> +{
> + struct extent_buffer *eb;
> + u32 nr;
> + int i;
> + int ret = 0;
> +
> + eb = read_tree_block(fs_info, parent, 0);
> + if (!extent_buffer_uptodate(eb)) {
> + ret = -EIO;
> + goto out;
> + }
> +
> + nr = btrfs_header_nritems(eb);
> + for (i = 0; i < nr; i++) {
> + struct btrfs_key key;
> + struct btrfs_file_extent_item *fi;
> + int extent_type;
> +
> + btrfs_item_key_to_cpu(eb, &key, i);
> + if (key.type != BTRFS_EXTENT_DATA_KEY)
> + continue;
> +
> + fi = btrfs_item_ptr(eb, i, struct btrfs_file_extent_item);
> + extent_type = btrfs_file_extent_type(eb, fi);
> + if (extent_type != BTRFS_FILE_EXTENT_REG &&
> + extent_type != BTRFS_FILE_EXTENT_PREALLOC)
> + continue;
> +
> + if (btrfs_file_extent_disk_bytenr(eb, fi) == disk_bytenr &&
> + extent_type == BTRFS_FILE_EXTENT_REG) {
> + ret = 1;
> + break;
> + }
> + }
> + out:
> + free_extent_buffer(eb);
> + return ret;
> +}
> +
> +/*
> + * Check if a prealloc extent is shared by multiple inodes and if any inode
> has
> + * already written to that extent. This is to avoid emitting invalid warnings
> + * about odd csum items (a inode has an extent entirely marked as prealloc
> + * but another inode shares it and has already written to it).
> + *
> + * Note: right now it does not check if the number of checksum items in the
> + * csum tree matches the number of bytes written into the ex-prealloc extent.
> + * It's complex to deal with that because the prealloc extent might have been
> + * partially written through multiple inodes and we would have to keep track
> of
> + * ranges, merging them and notice ranges that fully or partially overlap, to
> + * avoid false reports of csum items missing for areas of the prealloc extent
> + * that were not written to - for example if we have a 1M prealloc extent, we
> + * can have only the first half of it written, but 2 different inodes refer
> to
> + * the its first half (through reflinks/cloning), so keeping a counter of
> bytes
> + * covered by checksum items is not enough, as the correct value would be
> 512K
> + * and not 1M (whence the need to track ranges).
> + *
> + * Returns 0 if the prealloc extent was not written yet by any inode, 1 if
> + * at least one other inode has written to it, and < 0 on error.
> + */
> +int check_prealloc_extent_written(struct btrfs_fs_info *fs_info,
> + u64 disk_bytenr,
> + u64 num_bytes)
> +{
> + struct btrfs_path path;
> + struct btrfs_key key;
> + int ret;
> + struct btrfs_extent_item *ei;
> + u32 item_size;
> + unsigned long ptr;
> + unsigned long end;
> +
> + key.objectid = disk_bytenr;
> + key.type = BTRFS_EXTENT_ITEM_KEY;
> + key.offset = num_bytes;
> +
> + btrfs_init_path(&path);
> + ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, &path, 0, 0);
> + if (ret > 0) {
> + fprintf(stderr,
> + "Missing extent item in extent tree for disk_bytenr
> %llu, num_bytes %llu\n",
> + disk_bytenr, num_bytes);
> + ret = -ENOENT;
> + }
> + if (ret < 0)
> + goto out;
> +
> + /* First check all inline refs. */
> + ei = btrfs_item_ptr(path.nodes[0], path.slots[0],
> + struct btrfs_extent_item);
> + item_size = btrfs_item_size_nr(path.nodes[0], path.slots[0]);
> + ptr = (unsigned long)(ei + 1);
> + end = (unsigned long)ei + item_size;
> + while (ptr < end) {
> + struct btrfs_extent_inline_ref *iref;
> + int type;
> +
> + iref = (struct btrfs_extent_inline_ref *)ptr;
> + type = btrfs_extent_inline_ref_type(path.nodes[0], iref);
> + ASSERT(type == BTRFS_EXTENT_DATA_REF_KEY ||
> + type == BTRFS_SHARED_DATA_REF_KEY);
> +
> + if (type == BTRFS_EXTENT_DATA_REF_KEY) {
> + struct btrfs_extent_data_ref *dref;
> +
> + dref = (struct btrfs_extent_data_ref *)(&iref->offset);
> + ret = check_prealloc_data_ref(fs_info, disk_bytenr,
> + dref, path.nodes[0]);
> + if (ret != 0)
> + goto out;
> + } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
> + u64 parent;
> +
> + parent = btrfs_extent_inline_ref_offset(path.nodes[0],
> + iref);
> + ret = check_prealloc_shared_data_ref(fs_info,
> + parent,
> + disk_bytenr);
> + if (ret != 0)
> + goto out;
> + }
> +
> + ptr += btrfs_extent_inline_ref_size(type);
> + }
> +
> + /* Now check if there are any non-inlined refs. */
> + path.slots[0]++;
> + while (true) {
> + if (path.slots[0] >= btrfs_header_nritems(path.nodes[0])) {
> + ret = btrfs_next_leaf(fs_info->extent_root, &path);
> + if (ret < 0)
> + goto out;
> + if (ret > 0) {
> + ret = 0;
> + break;
> + }
> + }
> +
> + btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);
> + if (key.objectid != disk_bytenr)
> + break;
> +
> + if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
> + struct btrfs_extent_data_ref *dref;
> +
> + dref = btrfs_item_ptr(path.nodes[0], path.slots[0],
> + struct btrfs_extent_data_ref);
> + ret = check_prealloc_data_ref(fs_info, disk_bytenr,
> + dref, path.nodes[0]);
> + if (ret != 0)
> + goto out;
> + } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
> + ret = check_prealloc_shared_data_ref(fs_info,
> + key.offset,
> + disk_bytenr);
> + if (ret != 0)
> + goto out;
> + }
> +
> + path.slots[0]++;
> + }
> +out:
> + btrfs_release_path(&path);
> + return ret;
> +}
> +
> +/*
> * Search in csum tree to find how many bytes of range [@start, @start +
> @len)
> * has the corresponding csum item.
> *
> diff --git a/check/mode-common.h b/check/mode-common.h
> index ffae782b..79e1b0cf 100644
> --- a/check/mode-common.h
> +++ b/check/mode-common.h
> @@ -80,6 +80,9 @@ static inline int fs_root_objectid(u64 objectid)
> return is_fstree(objectid);
> }
>
> +int check_prealloc_extent_written(struct btrfs_fs_info *fs_info,
> + u64 disk_bytenr,
> + u64 num_bytes);
> int count_csum_range(struct btrfs_fs_info *fs_info, u64 start,
> u64 len, u64 *found);
> int insert_inode_item(struct btrfs_trans_handle *trans,
> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
> index 2424cdc2..02806377 100644
> --- a/check/mode-lowmem.c
> +++ b/check/mode-lowmem.c
> @@ -1511,9 +1511,17 @@ static int check_file_extent(struct btrfs_root *root,
> struct btrfs_key *fkey,
> csum_found, search_len);
> } else if (extent_type == BTRFS_FILE_EXTENT_PREALLOC &&
> csum_found > 0) {
> - err |= ODD_CSUM_ITEM;
> - error("root %llu EXTENT_DATA[%llu %llu] prealloc shouldn't have
> csum, but has: %llu",
> - root->objectid, fkey->objectid, fkey->offset, csum_found);
> + ret = check_prealloc_extent_written(root->fs_info,
> + disk_bytenr,
> + disk_num_bytes);
> + if (ret < 0)
> + return ret;
> + if (ret == 0) {
> + err |= ODD_CSUM_ITEM;
> + error("root %llu EXTENT_DATA[%llu %llu] prealloc
> shouldn't have csum, but has: %llu",
> + root->objectid, fkey->objectid, fkey->offset,
> + csum_found);
> + }
> }
>
> /* Check EXTENT_DATA hole */
>
--
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