On Thu, May 19, 2016 at 10:44 AM, Wang Xiaoguang
<wangxg.fnst@xxxxxxxxxxxxxx> wrote:
> In __btrfs_write_out_cache(), we don't call btrfs_delalloc_reserve_metadata()
> or btrfs_delalloc_reserve_space() to reserve metadata space, so we also should
> not call btrfs_delalloc_release_metadata(), in which BTRFS_I(inode)->outstanding_extents
> will be decreased, then WARN_ON(BTRFS_I(inode)->outstanding_extents) in
> btrfs_destroy_inode() will be triggered.
>
> To be honest, I do not see this WARNING in real, but I think we should fix it.
No, this is wrong.
We do this call to release reserved metadata space at
btrfs_save_ino_cache() through btrfs_delalloc_reserve_space().
And it's btrfs_save_ino_cache() that calls btrfs_write_out_ino_cache().
If what you said were true, then it would be trivial to write a test
case (using the inode cache feature) to trigger the problem.
>
> Signed-off-by: Wang Xiaoguang <wangxg.fnst@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/free-space-cache.c | 17 +++--------------
> 1 file changed, 3 insertions(+), 14 deletions(-)
>
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 8f835bf..ababf56 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -3512,7 +3512,6 @@ int btrfs_write_out_ino_cache(struct btrfs_root *root,
> struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
> int ret;
> struct btrfs_io_ctl io_ctl;
> - bool release_metadata = true;
>
> if (!btrfs_test_opt(root, INODE_MAP_CACHE))
> return 0;
> @@ -3520,26 +3519,16 @@ int btrfs_write_out_ino_cache(struct btrfs_root *root,
> memset(&io_ctl, 0, sizeof(io_ctl));
> ret = __btrfs_write_out_cache(root, inode, ctl, NULL, &io_ctl,
> trans, path, 0);
> - if (!ret) {
> - /*
> - * At this point writepages() didn't error out, so our metadata
> - * reservation is released when the writeback finishes, at
> - * inode.c:btrfs_finish_ordered_io(), regardless of it finishing
> - * with or without an error.
> - */
> - release_metadata = false;
> + if (!ret)
> ret = btrfs_wait_cache_io(root, trans, NULL, &io_ctl, path, 0);
> - }
>
> - if (ret) {
> - if (release_metadata)
> - btrfs_delalloc_release_metadata(inode, inode->i_size);
> #ifdef DEBUG
> + if (ret) {
> btrfs_err(root->fs_info,
> "failed to write free ino cache for root %llu",
> root->root_key.objectid);
> -#endif
> }
> +#endif
>
> return ret;
> }
> --
> 1.8.3.1
>
>
>
> --
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"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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