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ebb929060a
When we are doing a full fsync (bit BTRFS_INODE_NEEDS_FULL_SYNC set) of a
file that has holes and has file extent items spanning two or more leafs,
we can end up falling to back to a full transaction commit due to a logic
bug that leads to failure to insert a duplicate file extent item that is
meant to represent a hole between the last file extent item of a leaf and
the first file extent item in the next leaf. The failure (EEXIST error)
leads to a transaction commit (as most errors when logging an inode do).
For example, we have the two following leafs:
Leaf N:
-----------------------------------------------
| ..., ..., ..., (257, FILE_EXTENT_ITEM, 64K) |
-----------------------------------------------
The file extent item at the end of leaf N has a length of 4Kb,
representing the file range from 64K to 68K - 1.
Leaf N + 1:
-----------------------------------------------
| (257, FILE_EXTENT_ITEM, 72K), ..., ..., ... |
-----------------------------------------------
The file extent item at the first slot of leaf N + 1 has a length of
4Kb too, representing the file range from 72K to 76K - 1.
During the full fsync path, when we are at tree-log.c:copy_items() with
leaf N as a parameter, after processing the last file extent item, that
represents the extent at offset 64K, we take a look at the first file
extent item at the next leaf (leaf N + 1), and notice there's a 4K hole
between the two extents, and therefore we insert a file extent item
representing that hole, starting at file offset 68K and ending at offset
72K - 1. However we don't update the value of *last_extent, which is used
to represent the end offset (plus 1, non-inclusive end) of the last file
extent item inserted in the log, so it stays with a value of 68K and not
with a value of 72K.
Then, when copy_items() is called for leaf N + 1, because the value of
*last_extent is smaller then the offset of the first extent item in the
leaf (68K < 72K), we look at the last file extent item in the previous
leaf (leaf N) and see it there's a 4K gap between it and our first file
extent item (again, 68K < 72K), so we decide to insert a file extent item
representing the hole, starting at file offset 68K and ending at offset
72K - 1, this insertion will fail with -EEXIST being returned from
btrfs_insert_file_extent() because we already inserted a file extent item
representing a hole for this offset (68K) in the previous call to
copy_items(), when processing leaf N.
The -EEXIST error gets propagated to the fsync callback, btrfs_sync_file(),
which falls back to a full transaction commit.
Fix this by adjusting *last_extent after inserting a hole when we had to
look at the next leaf.
Fixes:
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.. | ||
tests | ||
acl.c | ||
async-thread.c | ||
async-thread.h | ||
backref.c | ||
backref.h | ||
btrfs_inode.h | ||
check-integrity.c | ||
check-integrity.h | ||
compression.c | ||
compression.h | ||
ctree.c | ||
ctree.h | ||
dedupe.h | ||
delayed-inode.c | ||
delayed-inode.h | ||
delayed-ref.c | ||
delayed-ref.h | ||
dev-replace.c | ||
dev-replace.h | ||
dir-item.c | ||
disk-io.c | ||
disk-io.h | ||
export.c | ||
export.h | ||
extent_io.c | ||
extent_io.h | ||
extent_map.c | ||
extent_map.h | ||
extent-tree.c | ||
file-item.c | ||
file.c | ||
free-space-cache.c | ||
free-space-cache.h | ||
free-space-tree.c | ||
free-space-tree.h | ||
inode-item.c | ||
inode-map.c | ||
inode-map.h | ||
inode.c | ||
ioctl.c | ||
Kconfig | ||
locking.c | ||
locking.h | ||
lzo.c | ||
Makefile | ||
math.h | ||
ordered-data.c | ||
ordered-data.h | ||
orphan.c | ||
print-tree.c | ||
print-tree.h | ||
props.c | ||
props.h | ||
qgroup.c | ||
qgroup.h | ||
raid56.c | ||
raid56.h | ||
rcu-string.h | ||
reada.c | ||
ref-verify.c | ||
ref-verify.h | ||
relocation.c | ||
root-tree.c | ||
scrub.c | ||
send.c | ||
send.h | ||
struct-funcs.c | ||
super.c | ||
sysfs.c | ||
sysfs.h | ||
transaction.c | ||
transaction.h | ||
tree-checker.c | ||
tree-checker.h | ||
tree-defrag.c | ||
tree-log.c | ||
tree-log.h | ||
ulist.c | ||
ulist.h | ||
uuid-tree.c | ||
volumes.c | ||
volumes.h | ||
xattr.c | ||
xattr.h | ||
zlib.c | ||
zstd.c |