[Ocfs2-devel] [PATCH] ocfs2: don't merge rightmost extent block if it was locked

[alex chen]

Hi Changwei,

On 2017/12/22 14:41, Changwei Ge wrote:
> A crash issue was reported by John.
> 
> The call trace follows:
> ocfs2_split_extent+0x1ad3/0x1b40 [ocfs2]
> ocfs2_change_extent_flag+0x33a/0x470 [ocfs2]
> ocfs2_mark_extent_written+0x172/0x220 [ocfs2]
> ocfs2_dio_end_io+0x62d/0x910 [ocfs2]
> dio_complete+0x19a/0x1a0
> do_blockdev_direct_IO+0x19dd/0x1eb0
> __blockdev_direct_IO+0x43/0x50
> ocfs2_direct_IO+0x8f/0xa0 [ocfs2]
> generic_file_direct_write+0xb2/0x170
> __generic_file_write_iter+0xc3/0x1b0
> ocfs2_file_write_iter+0x4bb/0xca0 [ocfs2]
> __vfs_write+0xae/0xf0
> vfs_write+0xb8/0x1b0
> SyS_write+0x4f/0xb0
> system_call_fastpath+0x16/0x75
> 
> The BUG code told that extent tree wants to grow but no metadata
> was reserved ahead of time.
>  From my investigation into this issue, the root cause it that although
> enough metadata is reserved, rightmost extent is merged into left one
> due to a certain times of marking extent written. Because during marking
> extent written, we got many physically continuous extents. At last, an
> empty extent showed up and the rightmost path is removed from extent tree.
> 
> In order to solve this issue, introduce a member named ::et_lock for extent
> tree. When ocfs2_lock_allocators is invoked and we indeed need to reserve
> metadata, set ::et_lock so that the rightmost path won't be removed during
> marking extents written.
> 
> Also, this patch address the issue John reported that ::dw_zero_count is
> not calculated properly.
> 
> After applying this patch, the issue John reported was gone.
> Thanks to the reproducer provided by John.
> And this patch has passed ocfs2-test suite running by New H3C Group.
> 
> Reported-by: John Lightsey <john at nixnuts.net>
> Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
> ---
>   fs/ocfs2/alloc.c    | 4 +++-
>   fs/ocfs2/alloc.h    | 1 +
>   fs/ocfs2/aops.c     | 8 +++++---
>   fs/ocfs2/suballoc.c | 3 +++
>   4 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index ab5105f..160e393 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -444,6 +444,7 @@ static void __ocfs2_init_extent_tree(struct ocfs2_extent_tree *et,
>   	et->et_ops = ops;
>   	et->et_root_bh = bh;
>   	et->et_ci = ci;
> +	et->et_lock = 0;
>   	et->et_root_journal_access = access;
>   	if (!obj)
>   		obj = (void *)bh->b_data;
> @@ -3606,7 +3607,8 @@ static int ocfs2_merge_rec_left(struct ocfs2_path *right_path,
>   		 * it and we need to delete the right extent block.
>   		 */
>   		if (le16_to_cpu(right_rec->e_leaf_clusters) == 0 &&
> -		    le16_to_cpu(el->l_next_free_rec) == 1) {
> +				le16_to_cpu(el->l_next_free_rec) == 1 &&
> +				!et->et_lock) {
>   			/* extend credit for ocfs2_remove_rightmost_path */
>   			ret = ocfs2_extend_rotate_transaction(handle, 0,
>   					handle->h_buffer_credits,
If we don't remove the rightmost path when we are splitting extents, when we should do it?
Does this break the balance of the extent tree?

> diff --git a/fs/ocfs2/alloc.h b/fs/ocfs2/alloc.h
> index 27b75cf..898671d 100644
> --- a/fs/ocfs2/alloc.h
> +++ b/fs/ocfs2/alloc.h
> @@ -61,6 +61,7 @@ struct ocfs2_extent_tree {
>   	ocfs2_journal_access_func		et_root_journal_access;
>   	void					*et_object;
>   	unsigned int				et_max_leaf_clusters;
> +	int					et_lock;
>   };
>   
>   /*
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index d151632..c72ce60 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c
> @@ -797,6 +797,7 @@ struct ocfs2_write_ctxt {
>   	struct ocfs2_cached_dealloc_ctxt w_dealloc;
>   
>   	struct list_head		w_unwritten_list;
> +	unsigned int			w_unwritten_count;
>   };
>   
>   void ocfs2_unlock_and_free_pages(struct page **pages, int num_pages)
> @@ -1386,6 +1387,7 @@ static int ocfs2_unwritten_check(struct inode *inode,
>   	desc->c_clear_unwritten = 0;
>   	list_add_tail(&new->ue_ip_node, &oi->ip_unwritten_list);
>   	list_add_tail(&new->ue_node, &wc->w_unwritten_list);
> +	wc->w_unwritten_count++;
>   	new = NULL;
>   unlock:
>   	spin_unlock(&oi->ip_lock);
> @@ -1762,8 +1764,8 @@ int ocfs2_write_begin_nolock(struct address_space *mapping,
>   		 */
>   		ocfs2_init_dinode_extent_tree(&et, INODE_CACHE(inode),
>   					      wc->w_di_bh);
> -		ret = ocfs2_lock_allocators(inode, &et,
> -					    clusters_to_alloc, extents_to_split,
> +		ret = ocfs2_lock_allocators(inode, &et, clusters_to_alloc,
> +					    2*extents_to_split,
>   					    &data_ac, &meta_ac);
>   		if (ret) {
>   			mlog_errno(ret);
> @@ -2256,7 +2258,7 @@ static int ocfs2_dio_wr_get_block(struct inode *inode, sector_t iblock,
>   		ue->ue_phys = desc->c_phys;
>   
>   		list_splice_tail_init(&wc->w_unwritten_list, &dwc->dw_zero_list);
> -		dwc->dw_zero_count++;
> +		dwc->dw_zero_count += wc->w_unwritten_count;
>   	}
>   
>   	ret = ocfs2_write_end_nolock(inode->i_mapping, pos, len, len, wc);
> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> index 9f0b95a..32bc38e 100644
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> @@ -2727,6 +2727,9 @@ int ocfs2_lock_allocators(struct inode *inode,
>   		}
>   	}
>   
> +	if (extents_to_split)
> +		et->et_lock = 1;
> +
If we remove the xattr cluster we need to split the extent in ocfs2_rm_xattr_cluster() and
why we should not remove the rightmost path?
Can we use the extents_to_split to identify we are marking extent written?

Thanks,
Alex

>   	if (clusters_to_add == 0)
>   		goto out;
>   
>