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authorFilipe Manana <fdmanana@suse.com>2020-04-23 16:30:53 +0100
committerDavid Sterba <dsterba@suse.com>2020-04-27 17:16:07 +0200
commitf135cea30de5f74d5bfb5116682073841fb4af8f (patch)
treefbead582f8ed3caf346ba950a6017134a0d7e0ab /fs/btrfs
parent1402d17dfd9657be0da8458b2079d03c2d61c86a (diff)
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btrfs: fix partial loss of prealloc extent past i_size after fsync
When we have an inode with a prealloc extent that starts at an offset lower than the i_size and there is another prealloc extent that starts at an offset beyond i_size, we can end up losing part of the first prealloc extent (the part that starts at i_size) and have an implicit hole if we fsync the file and then have a power failure. Consider the following example with comments explaining how and why it happens. $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt # Create our test file with 2 consecutive prealloc extents, each with a # size of 128Kb, and covering the range from 0 to 256Kb, with a file # size of 0. $ xfs_io -f -c "falloc -k 0 128K" /mnt/foo $ xfs_io -c "falloc -k 128K 128K" /mnt/foo # Fsync the file to record both extents in the log tree. $ xfs_io -c "fsync" /mnt/foo # Now do a redudant extent allocation for the range from 0 to 64Kb. # This will merely increase the file size from 0 to 64Kb. Instead we # could also do a truncate to set the file size to 64Kb. $ xfs_io -c "falloc 0 64K" /mnt/foo # Fsync the file, so we update the inode item in the log tree with the # new file size (64Kb). This also ends up setting the number of bytes # for the first prealloc extent to 64Kb. This is done by the truncation # at btrfs_log_prealloc_extents(). # This means that if a power failure happens after this, a write into # the file range 64Kb to 128Kb will not use the prealloc extent and # will result in allocation of a new extent. $ xfs_io -c "fsync" /mnt/foo # Now set the file size to 256K with a truncate and then fsync the file. # Since no changes happened to the extents, the fsync only updates the # i_size in the inode item at the log tree. This results in an implicit # hole for the file range from 64Kb to 128Kb, something which fsck will # complain when not using the NO_HOLES feature if we replay the log # after a power failure. $ xfs_io -c "truncate 256K" -c "fsync" /mnt/foo So instead of always truncating the log to the inode's current i_size at btrfs_log_prealloc_extents(), check first if there's a prealloc extent that starts at an offset lower than the i_size and with a length that crosses the i_size - if there is one, just make sure we truncate to a size that corresponds to the end offset of that prealloc extent, so that we don't lose the part of that extent that starts at i_size if a power failure happens. A test case for fstests follows soon. Fixes: 31d11b83b96f ("Btrfs: fix duplicate extents after fsync of file with prealloc extents") CC: stable@vger.kernel.org # 4.14+ Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
-rw-r--r--fs/btrfs/tree-log.c43
1 files changed, 40 insertions, 3 deletions
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index ec36a7c6ba3d..02ebdd9edc19 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4226,6 +4226,9 @@ static int btrfs_log_prealloc_extents(struct btrfs_trans_handle *trans,
const u64 ino = btrfs_ino(inode);
struct btrfs_path *dst_path = NULL;
bool dropped_extents = false;
+ u64 truncate_offset = i_size;
+ struct extent_buffer *leaf;
+ int slot;
int ins_nr = 0;
int start_slot;
int ret;
@@ -4240,9 +4243,43 @@ static int btrfs_log_prealloc_extents(struct btrfs_trans_handle *trans,
if (ret < 0)
goto out;
+ /*
+ * We must check if there is a prealloc extent that starts before the
+ * i_size and crosses the i_size boundary. This is to ensure later we
+ * truncate down to the end of that extent and not to the i_size, as
+ * otherwise we end up losing part of the prealloc extent after a log
+ * replay and with an implicit hole if there is another prealloc extent
+ * that starts at an offset beyond i_size.
+ */
+ ret = btrfs_previous_item(root, path, ino, BTRFS_EXTENT_DATA_KEY);
+ if (ret < 0)
+ goto out;
+
+ if (ret == 0) {
+ struct btrfs_file_extent_item *ei;
+
+ leaf = path->nodes[0];
+ slot = path->slots[0];
+ ei = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
+
+ if (btrfs_file_extent_type(leaf, ei) ==
+ BTRFS_FILE_EXTENT_PREALLOC) {
+ u64 extent_end;
+
+ btrfs_item_key_to_cpu(leaf, &key, slot);
+ extent_end = key.offset +
+ btrfs_file_extent_num_bytes(leaf, ei);
+
+ if (extent_end > i_size)
+ truncate_offset = extent_end;
+ }
+ } else {
+ ret = 0;
+ }
+
while (true) {
- struct extent_buffer *leaf = path->nodes[0];
- int slot = path->slots[0];
+ leaf = path->nodes[0];
+ slot = path->slots[0];
if (slot >= btrfs_header_nritems(leaf)) {
if (ins_nr > 0) {
@@ -4280,7 +4317,7 @@ static int btrfs_log_prealloc_extents(struct btrfs_trans_handle *trans,
ret = btrfs_truncate_inode_items(trans,
root->log_root,
&inode->vfs_inode,
- i_size,
+ truncate_offset,
BTRFS_EXTENT_DATA_KEY);
} while (ret == -EAGAIN);
if (ret)