4.16-stable review patch. If anyone has any objections, please let me know.
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From: Filipe Manana fdmanana@suse.com
[ Upstream commit 471d557afed155b85da237ec46c549f443eeb5de ]
Currently if we allocate extents beyond an inode's i_size (through the fallocate system call) and then fsync the file, we log the extents but after a power failure we replay them and then immediately drop them. This behaviour happens since about 2009, commit c71bf099abdd ("Btrfs: Avoid orphan inodes cleanup while replaying log"), because it marks the inode as an orphan instead of dropping any extents beyond i_size before replaying logged extents, so after the log replay, and while the mount operation is still ongoing, we find the inode marked as an orphan and then perform a truncation (drop extents beyond the inode's i_size). Because the processing of orphan inodes is still done right after replaying the log and before the mount operation finishes, the intention of that commit does not make any sense (at least as of today). However reverting that behaviour is not enough, because we can not simply discard all extents beyond i_size and then replay logged extents, because we risk dropping extents beyond i_size created in past transactions, for example:
add prealloc extent beyond i_size fsync - clears the flag BTRFS_INODE_NEEDS_FULL_SYNC from the inode transaction commit add another prealloc extent beyond i_size fsync - triggers the fast fsync path power failure
In that scenario, we would drop the first extent and then replay the second one. To fix this just make sure that all prealloc extents beyond i_size are logged, and if we find too many (which is far from a common case), fallback to a full transaction commit (like we do when logging regular extents in the fast fsync path).
Trivial reproducer:
$ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt $ xfs_io -f -c "pwrite -S 0xab 0 256K" /mnt/foo $ sync $ xfs_io -c "falloc -k 256K 1M" /mnt/foo $ xfs_io -c "fsync" /mnt/foo <power failure>
# mount to replay log $ mount /dev/sdb /mnt # at this point the file only has one extent, at offset 0, size 256K
A test case for fstests follows soon, covering multiple scenarios that involve adding prealloc extents with previous shrinking truncates and without such truncates.
Fixes: c71bf099abdd ("Btrfs: Avoid orphan inodes cleanup while replaying log") Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/tree-log.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 58 insertions(+), 5 deletions(-)
--- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -2461,13 +2461,41 @@ static int replay_one_buffer(struct btrf if (ret) break;
- /* for regular files, make sure corresponding - * orphan item exist. extents past the new EOF - * will be truncated later by orphan cleanup. + /* + * Before replaying extents, truncate the inode to its + * size. We need to do it now and not after log replay + * because before an fsync we can have prealloc extents + * added beyond the inode's i_size. If we did it after, + * through orphan cleanup for example, we would drop + * those prealloc extents just after replaying them. */ if (S_ISREG(mode)) { - ret = insert_orphan_item(wc->trans, root, - key.objectid); + struct inode *inode; + u64 from; + + inode = read_one_inode(root, key.objectid); + if (!inode) { + ret = -EIO; + break; + } + from = ALIGN(i_size_read(inode), + root->fs_info->sectorsize); + ret = btrfs_drop_extents(wc->trans, root, inode, + from, (u64)-1, 1); + /* + * If the nlink count is zero here, the iput + * will free the inode. We bump it to make + * sure it doesn't get freed until the link + * count fixup is done. + */ + if (!ret) { + if (inode->i_nlink == 0) + inc_nlink(inode); + /* Update link count and nbytes. */ + ret = btrfs_update_inode(wc->trans, + root, inode); + } + iput(inode); if (ret) break; } @@ -4321,6 +4349,31 @@ static int btrfs_log_changed_extents(str num++; }
+ /* + * Add all prealloc extents beyond the inode's i_size to make sure we + * don't lose them after doing a fast fsync and replaying the log. + */ + if (inode->flags & BTRFS_INODE_PREALLOC) { + struct rb_node *node; + + for (node = rb_last(&tree->map); node; node = rb_prev(node)) { + em = rb_entry(node, struct extent_map, rb_node); + if (em->start < i_size_read(&inode->vfs_inode)) + break; + if (!list_empty(&em->list)) + continue; + /* Same as above loop. */ + if (++num > 32768) { + list_del_init(&tree->modified_extents); + ret = -EFBIG; + goto process; + } + refcount_inc(&em->refs); + set_bit(EXTENT_FLAG_LOGGING, &em->flags); + list_add_tail(&em->list, &extents); + } + } + list_sort(NULL, &extents, extent_cmp); btrfs_get_logged_extents(inode, logged_list, logged_start, logged_end); /*