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authorFilipe Manana <fdmanana@suse.com>2014-08-25 10:43:00 +0100
committerChris Mason <clm@fb.com>2014-09-02 16:46:05 -0700
commitd9f85963e3f7f5582552fdae54a2b89d6c62daf5 (patch)
tree676942dbb75c27e47f8d2c3565c9c4b76832e2dc /fs
parente9512d72e8e61c750c90efacd720abe3c4569822 (diff)
downloadlinux-d9f85963e3f7f5582552fdae54a2b89d6c62daf5.tar.bz2
Btrfs: fix corruption after write/fsync failure + fsync + log recovery
While writing to a file, in inode.c:cow_file_range() (and same applies to submit_compressed_extents()), after reserving an extent for the file data, we create a new extent map for the written range and insert it into the extent map cache. After that, we create an ordered operation, but if it fails (due to a transient/temporary-ENOMEM), we return without dropping that extent map, which points to a reserved extent that is freed when we return. A subsequent incremental fsync (when the btrfs inode doesn't have the flag BTRFS_INODE_NEEDS_FULL_SYNC) considers this extent map valid and logs a file extent item based on that extent map, which points to a disk extent that doesn't contain valid data - it was freed by us earlier, at this point it might contain any random/garbage data. Therefore, if we reach an error condition when cowing a file range after we added the new extent map to the cache, drop it from the cache before returning. Some sequence of steps that lead to this: $ mkfs.btrfs -f /dev/sdd $ mount -o commit=9999 /dev/sdd /mnt $ cd /mnt $ xfs_io -f -c "pwrite -S 0x01 -b 4096 0 4096" -c "fsync" foo $ xfs_io -c "pwrite -S 0x02 -b 4096 4096 4096" $ sync $ od -t x1 foo 0000000 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 * 0010000 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 * 0020000 $ xfs_io -c "pwrite -S 0xa1 -b 4096 0 4096" foo # Now this write + fsync fail with -ENOMEM, which was returned by # btrfs_add_ordered_extent() in inode.c:cow_file_range(). $ xfs_io -c "pwrite -S 0xff -b 4096 4096 4096" foo $ xfs_io -c "fsync" foo fsync: Cannot allocate memory # Now do a new write + fsync, which will succeed. Our previous # -ENOMEM was a transient/temporary error. $ xfs_io -c "pwrite -S 0xee -b 4096 16384 4096" foo $ xfs_io -c "fsync" foo # Our file content (in page cache) is now: $ od -t x1 foo 0000000 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 a1 * 0010000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0020000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 0040000 ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee * 0050000 # Now reboot the machine, and mount the fs, so that fsync log replay # takes place. # The file content is now weird, in particular the first 8Kb, which # do not match our data before nor after the sync command above. $ od -t x1 foo 0000000 ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee * 0010000 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 * 0020000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 0040000 ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee * 0050000 # In fact these first 4Kb are a duplicate of the last 4kb block. # The last write got an extent map/file extent item that points to # the same disk extent that we got in the write+fsync that failed # with the -ENOMEM error. btrfs-debug-tree and btrfsck allow us to # verify that: $ btrfs-debug-tree /dev/sdd (...) item 6 key (257 EXTENT_DATA 0) itemoff 15819 itemsize 53 extent data disk byte 12582912 nr 8192 extent data offset 0 nr 8192 ram 8192 item 7 key (257 EXTENT_DATA 8192) itemoff 15766 itemsize 53 extent data disk byte 0 nr 0 extent data offset 0 nr 8192 ram 8192 item 8 key (257 EXTENT_DATA 16384) itemoff 15713 itemsize 53 extent data disk byte 12582912 nr 4096 extent data offset 0 nr 4096 ram 4096 $ umount /dev/sdd $ btrfsck /dev/sdd Checking filesystem on /dev/sdd UUID: db5e60e1-050d-41e6-8c7f-3d742dea5d8f checking extents extent item 12582912 has multiple extent items ref mismatch on [12582912 4096] extent item 1, found 2 Backref bytes do not match extent backref, bytenr=12582912, ref bytes=4096, backref bytes=8192 backpointer mismatch on [12582912 4096] Errors found in extent allocation tree or chunk allocation checking free space cache checking fs roots root 5 inode 257 errors 1000, some csum missing found 131074 bytes used err is 1 total csum bytes: 4 total tree bytes: 131072 total fs tree bytes: 32768 total extent tree bytes: 16384 btree space waste bytes: 123404 file data blocks allocated: 274432 referenced 274432 Btrfs v3.14.1-96-gcc7fd5a-dirty Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/inode.c12
1 files changed, 9 insertions, 3 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3d020d6d9ace..7313571e1860 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -778,8 +778,12 @@ retry:
ins.offset,
BTRFS_ORDERED_COMPRESSED,
async_extent->compress_type);
- if (ret)
+ if (ret) {
+ btrfs_drop_extent_cache(inode, async_extent->start,
+ async_extent->start +
+ async_extent->ram_size - 1, 0);
goto out_free_reserve;
+ }
/*
* clear dirty, set writeback and unlock the pages.
@@ -971,14 +975,14 @@ static noinline int cow_file_range(struct inode *inode,
ret = btrfs_add_ordered_extent(inode, start, ins.objectid,
ram_size, cur_alloc_size, 0);
if (ret)
- goto out_reserve;
+ goto out_drop_extent_cache;
if (root->root_key.objectid ==
BTRFS_DATA_RELOC_TREE_OBJECTID) {
ret = btrfs_reloc_clone_csums(inode, start,
cur_alloc_size);
if (ret)
- goto out_reserve;
+ goto out_drop_extent_cache;
}
if (disk_num_bytes < cur_alloc_size)
@@ -1006,6 +1010,8 @@ static noinline int cow_file_range(struct inode *inode,
out:
return ret;
+out_drop_extent_cache:
+ btrfs_drop_extent_cache(inode, start, start + ram_size - 1, 0);
out_reserve:
btrfs_free_reserved_extent(root, ins.objectid, ins.offset, 1);
out_unlock: