From: Filipe Manana fdmanana@suse.com
[ Upstream commit cceaa89f02f15f232391ae4be214137b0a0285c0 ]
When using the NO_HOLES feature and expanding the size of an inode, we update the inode's last_trans, last_sub_trans and last_log_commit fields at maybe_insert_hole() so that a fsync does know that the inode needs to be logged (by making sure that btrfs_inode_in_log() returns false). This happens for expanding truncate operations, buffered writes, direct IO writes and when cloning extents to an offset greater than the inode's i_size.
However the way we do it is racy, because in between setting the inode's last_sub_trans and last_log_commit fields, the log transaction ID that was assigned to last_sub_trans might be committed before we read the root's last_log_commit and assign that value to last_log_commit. If that happens it would make a future call to btrfs_inode_in_log() return true. This is a race that should be extremely unlikely to be hit in practice, and it is the same that was described by commit bc0939fcfab0d7 ("btrfs: fix race between marking inode needs to be logged and log syncing").
The fix would simply be to set last_log_commit to the value we assigned to last_sub_trans minus 1, like it was done in that commit. However updating these two fields plus the last_trans field is pointless here because all the callers of btrfs_cont_expand() (which is the only caller of maybe_insert_hole()) always call btrfs_set_inode_last_trans() or btrfs_update_inode() after calling btrfs_cont_expand(). Calling either btrfs_set_inode_last_trans() or btrfs_update_inode() guarantees that the next fsync will log the inode, as it makes btrfs_inode_in_log() return false.
So just remove the code that explicitly sets the inode's last_trans, last_sub_trans and last_log_commit fields.
Reviewed-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/inode.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 4fd242acec3c..8132d503c83d 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5088,15 +5088,13 @@ static int maybe_insert_hole(struct btrfs_root *root, struct btrfs_inode *inode, int ret;
/* - * Still need to make sure the inode looks like it's been updated so - * that any holes get logged if we fsync. + * If NO_HOLES is enabled, we don't need to do anything. + * Later, up in the call chain, either btrfs_set_inode_last_sub_trans() + * or btrfs_update_inode() will be called, which guarantee that the next + * fsync will know this inode was changed and needs to be logged. */ - if (btrfs_fs_incompat(fs_info, NO_HOLES)) { - inode->last_trans = fs_info->generation; - inode->last_sub_trans = root->log_transid; - inode->last_log_commit = root->last_log_commit; + if (btrfs_fs_incompat(fs_info, NO_HOLES)) return 0; - }
/* * 1 - for the one we're dropping