On Fri, Sep 28, 2018 at 12:19 PM Josef Bacik <josef@xxxxxxxxxxxxxx> wrote:
>
> We're getting a lockdep splat because we take the dio_sem under the
> log_mutex. What we really need is to protect fsync() from logging an
> extent map for an extent we never waited on higher up, so just guard the
> whole thing with dio_sem.
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Looks good, thanks. However as David said, it would be nice to have a
sample trace pasted in the changelog (several fstests test cases
trigger this often).
> ---
> fs/btrfs/file.c | 12 ++++++++++++
> fs/btrfs/tree-log.c | 2 --
> 2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 095f0bb86bb7..c07110edb9de 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -2079,6 +2079,14 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> goto out;
>
> inode_lock(inode);
> +
> + /*
> + * We take the dio_sem here because the tree log stuff can race with
> + * lockless dio writes and get an extent map logged for an extent we
> + * never waited on. We need it this high up for lockdep reasons.
> + */
> + down_write(&BTRFS_I(inode)->dio_sem);
> +
> atomic_inc(&root->log_batch);
>
> /*
> @@ -2087,6 +2095,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> */
> ret = btrfs_wait_ordered_range(inode, start, len);
> if (ret) {
> + up_write(&BTRFS_I(inode)->dio_sem);
> inode_unlock(inode);
> goto out;
> }
> @@ -2110,6 +2119,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> * checked called fsync.
> */
> ret = filemap_check_wb_err(inode->i_mapping, file->f_wb_err);
> + up_write(&BTRFS_I(inode)->dio_sem);
> inode_unlock(inode);
> goto out;
> }
> @@ -2128,6 +2138,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> trans = btrfs_start_transaction(root, 0);
> if (IS_ERR(trans)) {
> ret = PTR_ERR(trans);
> + up_write(&BTRFS_I(inode)->dio_sem);
> inode_unlock(inode);
> goto out;
> }
> @@ -2149,6 +2160,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> * file again, but that will end up using the synchronization
> * inside btrfs_sync_log to keep things safe.
> */
> + up_write(&BTRFS_I(inode)->dio_sem);
> inode_unlock(inode);
>
> /*
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 1650dc44a5e3..66b7e059b765 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -4374,7 +4374,6 @@ static int btrfs_log_changed_extents(struct btrfs_trans_handle *trans,
>
> INIT_LIST_HEAD(&extents);
>
> - down_write(&inode->dio_sem);
> write_lock(&tree->lock);
> test_gen = root->fs_info->last_trans_committed;
> logged_start = start;
> @@ -4440,7 +4439,6 @@ static int btrfs_log_changed_extents(struct btrfs_trans_handle *trans,
> }
> WARN_ON(!list_empty(&extents));
> write_unlock(&tree->lock);
> - up_write(&inode->dio_sem);
>
> btrfs_release_path(path);
> if (!ret)
> --
> 2.14.3
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
