Hi Changwei,

On 2017/12/26 14:22, 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 not reserved, there should be enough for following use.
> Rightmost extent is merged into its 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.
> 
> Add a new mechanism to reuse extent block cached in dealloc which were
> just unlinked from extent tree to solve this crash issue.
> 
> Criteria is that during marking extents *written*, if extent rotation
> and merging results in unlinking extent with growing extent tree later
> without any metadata reserved ahead of time, try to reuse those extents
> in dealloc in which deleted extents are cached.
How can you guarantee that those extent blocks cached by removed the rightmost 
path
are enough for next growing extent tree?

> 
> Also, this patch addresses the issue John reported that ::dw_zero_count is
> not calculated properly.
> 
> After applying this patch, the issue John reported was gone.
> Thanks for the reproducer provided by John.
> And this patch has passed ocfs2-test(29 cases) suite running by New H3C Group.
> 
> Reported-by: John Lightsey <j...@nixnuts.net>
> Signed-off-by: Changwei Ge <ge.chang...@h3c.com>
> ---
>   fs/ocfs2/alloc.c | 128 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++---
>   fs/ocfs2/alloc.h |   1 +
>   fs/ocfs2/aops.c  |  14 ++++--
>   3 files changed, 135 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index ab5105f..eb41074 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -165,6 +165,13 @@ static int ocfs2_dinode_insert_check(struct 
> ocfs2_extent_tree *et,
>                                    struct ocfs2_extent_rec *rec);
>   static int ocfs2_dinode_sanity_check(struct ocfs2_extent_tree *et);
>   static void ocfs2_dinode_fill_root_el(struct ocfs2_extent_tree *et);
> +
> +static int ocfs2_reuse_blk_from_dealloc(handle_t *handle,
> +                                     struct ocfs2_extent_tree *et,
> +                                     struct buffer_head **new_eb_bh,
> +                                     int blk_cnt);
> +static int ocfs2_is_dealloc_empty(struct ocfs2_extent_tree *et);
> +
>   static const struct ocfs2_extent_tree_operations ocfs2_dinode_et_ops = {
>       .eo_set_last_eb_blk     = ocfs2_dinode_set_last_eb_blk,
>       .eo_get_last_eb_blk     = ocfs2_dinode_get_last_eb_blk,
> @@ -448,6 +455,7 @@ static void __ocfs2_init_extent_tree(struct 
> ocfs2_extent_tree *et,
>       if (!obj)
>               obj = (void *)bh->b_data;
>       et->et_object = obj;
> +     et->et_dealloc = NULL;
>   
>       et->et_ops->eo_fill_root_el(et);
>       if (!et->et_ops->eo_fill_max_leaf_clusters)
> @@ -1213,8 +1221,15 @@ static int ocfs2_add_branch(handle_t *handle,
>               goto bail;
>       }
>   
> -     status = ocfs2_create_new_meta_bhs(handle, et, new_blocks,
> -                                        meta_ac, new_eb_bhs);
> +     if (meta_ac) {
> +             status = ocfs2_create_new_meta_bhs(handle, et, new_blocks,
> +                                                meta_ac, new_eb_bhs);
> +     } else if (!ocfs2_is_dealloc_empty(et)) {
> +             status = ocfs2_reuse_blk_from_dealloc(handle, et,
> +                                                   new_eb_bhs, new_blocks);
> +     } else {
> +             BUG();
> +     }
>       if (status < 0) {
>               mlog_errno(status);
>               goto bail;
> @@ -1347,8 +1362,15 @@ static int ocfs2_shift_tree_depth(handle_t *handle,
>       struct ocfs2_extent_list  *root_el;
>       struct ocfs2_extent_list  *eb_el;
>   
> -     status = ocfs2_create_new_meta_bhs(handle, et, 1, meta_ac,
> -                                        &new_eb_bh);
> +     if (meta_ac) {
> +             status = ocfs2_create_new_meta_bhs(handle, et, 1, meta_ac,
> +                                                &new_eb_bh);
> +     } else if (!ocfs2_is_dealloc_empty(et)) {
> +             status = ocfs2_reuse_blk_from_dealloc(handle, et,
> +                                                   &new_eb_bh, 1);
> +     } else {
> +             BUG();
> +     }
>       if (status < 0) {
>               mlog_errno(status);
>               goto bail;
> @@ -1511,7 +1533,7 @@ static int ocfs2_grow_tree(handle_t *handle, struct 
> ocfs2_extent_tree *et,
>       int depth = le16_to_cpu(el->l_tree_depth);
>       struct buffer_head *bh = NULL;
>   
> -     BUG_ON(meta_ac == NULL);
> +     BUG_ON(meta_ac == NULL && ocfs2_is_dealloc_empty(et));
>   
>       shift = ocfs2_find_branch_target(et, &bh);
>       if (shift < 0) {
> @@ -6585,6 +6607,102 @@ ocfs2_find_per_slot_free_list(int type,
>       return fl;
>   }
>   
> +/* Return Value 1 indicates empty */
> +static int ocfs2_is_dealloc_empty(struct ocfs2_extent_tree *et)
> +{
> +     struct ocfs2_per_slot_free_list *fl;
> +     struct ocfs2_super *osb =
> +             OCFS2_SB(ocfs2_metadata_cache_get_super(et->et_ci));
> +
> +     if (!et->et_dealloc)
> +             return 1;
> +
> +     fl = ocfs2_find_per_slot_free_list(EXTENT_ALLOC_SYSTEM_INODE,
> +                                        osb->slot_num, et->et_dealloc);
> +
> +     return fl ? 0 : 1;
> +}
> +
> +/* If extent was deleted from tree due to extent rotation and merging, and
> + * no metadata is reserved ahead of time. Try to reuse some extents
> + * just deleted. This is only used to reuse extent blocks.
> + * It is supposed to find enough extent blocks in dealloc if our estimation
> + * on metadata is accurate.
> + */
> +static int ocfs2_reuse_blk_from_dealloc(handle_t *handle,
> +                                     struct ocfs2_extent_tree *et,
> +                                     struct buffer_head **new_eb_bh,
> +                                     int blk_cnt)
> +{
> +     int i, status = -ENOSPC;
> +     struct ocfs2_cached_dealloc_ctxt *dealloc;
> +     struct ocfs2_per_slot_free_list *fl;
> +     struct ocfs2_cached_block_free *bf;
> +     struct ocfs2_extent_block *eb;
> +     struct ocfs2_super *osb =
> +             OCFS2_SB(ocfs2_metadata_cache_get_super(et->et_ci));
> +
> +     dealloc = et->et_dealloc;
> +     if (!dealloc)
> +             goto bail;
> +
> +     for (i = 0; i < blk_cnt; i++) {
> +             fl = ocfs2_find_per_slot_free_list(EXTENT_ALLOC_SYSTEM_INODE,
> +                                                osb->slot_num, dealloc);
> +             /* The caller should guarantee that dealloc has cached some
> +              * extent blocks.
> +              */
> +             BUG_ON(!fl);
> +
It is too crude to BUGON here.

> +             dealloc->c_first_suballocator = fl->f_next_suballocator;
> +             bf = fl->f_first;
> +             new_eb_bh[i] = sb_getblk(osb->sb, bf->free_blk);
> +             if (new_eb_bh[i] == NULL) {
> +                     status = -ENOMEM;
> +                     mlog_errno(status);
> +                     goto bail;
> +             }
> +
> +             mlog(0, "Reusing block(%llu) from dealloc\n", bf->free_blk);
> +
> +             ocfs2_set_new_buffer_uptodate(et->et_ci, new_eb_bh[i]);
> +
> +             status = ocfs2_journal_access_eb(handle, et->et_ci,
> +                                              new_eb_bh[i],
> +                                              OCFS2_JOURNAL_ACCESS_CREATE);
> +             if (status < 0) {
> +                     mlog_errno(status);
> +                     goto bail;
> +             }
> +
> +             memset(new_eb_bh[i]->b_data, 0, osb->sb->s_blocksize);
> +             eb = (struct ocfs2_extent_block *) new_eb_bh[i]->b_data;
> +
> +             /* We can't guarantee that buffer head is still cached, so
> +              * polutlate the extent block again.
> +              */
> +             strcpy(eb->h_signature, OCFS2_EXTENT_BLOCK_SIGNATURE);
> +             eb->h_blkno = cpu_to_le64(bf->free_blk);
> +             eb->h_fs_generation = cpu_to_le32(osb->fs_generation);
> +             eb->h_suballoc_slot = cpu_to_le16(osb->slot_num);
> +             eb->h_suballoc_loc = cpu_to_le64(bf->free_bg);
> +             eb->h_suballoc_bit = cpu_to_le16(bf->free_bit);
> +             eb->h_list.l_count =
> +                     cpu_to_le16(ocfs2_extent_recs_per_eb(osb->sb));
> +
> +             /* We'll also be dirtied by the caller, so
> +              * this isn't absolutely necessary.
> +              */
> +             ocfs2_journal_dirty(handle, new_eb_bh[i]);
> +
> +             kfree(fl);
> +             kfree(bf);
> +     }
> +
> +bail:
> +     return status;
> +}
> +
>   int ocfs2_cache_block_dealloc(struct ocfs2_cached_dealloc_ctxt *ctxt,
>                             int type, int slot, u64 suballoc,
>                             u64 blkno, unsigned int bit)
> diff --git a/fs/ocfs2/alloc.h b/fs/ocfs2/alloc.h
> index 27b75cf..250bcac 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;
> +     struct ocfs2_cached_dealloc_ctxt        *et_dealloc;
>   };
>   
>   /*
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index d151632..1bbd5c8 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,
Why here is 2*extents_to_split not 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);
> @@ -2330,6 +2332,12 @@ static int ocfs2_dio_end_io_write(struct inode *inode,
>   
>       ocfs2_init_dinode_extent_tree(&et, INODE_CACHE(inode), di_bh);
>   
> +     /* Attach dealloc with extent tree in case that we may reuse extents
> +      * which are already unlinked from current extent tree due to extent
> +      * rotation and merging.
> +      */
> +     et.et_dealloc = &dealloc;
> +
>       ret = ocfs2_lock_allocators(inode, &et, 0, dwc->dw_zero_count*2,
>                                   &data_ac, &meta_ac);
>       if (ret) {
> 


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