Hi Junxiao,
On 2017/12/27 18:02, Junxiao Bi wrote:
> Hi Changwei,
>
>
> On 12/26/2017 03:55 PM, 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.
> I am trying to understand the issue. Quick questions.
> Is this issue caused by BUG_ON(meta_ac == NULL)? Can you explain why it
> is NULL?
My pleasure to.
Before marking extents written, we have to estimate how many metadata will be
used.
If there are enough metadata for following operation-marking extent written, no
metadata
will be reserved ahead of time.
For this BUG scenario, it happens that extent tree already has enough free
metadata.
This can be referred by code path:
ocfs2_dio_end_io_write
ocfs2_lock_allocators - No need to reserve metadata,since extent tree
already has more metadata than needed. So *mata_ac* is NULL.
ocfs2_mark_extent_written
ocfs2_change_extent_flag - cluster by cluster
ocfs2_split_extent
ocfs2_try_to_merge_extent - During filling file hole, we mark cluster
as written one by one. Somehow, we merge those physically continuous
cluster(WRITTEN) into a single one.
ocfs2_rotate_tree_left - rotate extent
__ocfs2_rotate_tree_left
ocfs2_rotate_subtree_left - Aha, we find a totally empty extent
here, so unlink it from extent tree.
ocfs2_unlink_subtree
ocfs2_remove_empty_extent
Then, since we delete one extent block, our previously estimated metadata
number is
pointless(NOTE, actually the estimation is accurate.). Since it is reduced
resulted by extent
rotation and merging.
So for now, we don't have enough metadata.
Then we are still marking extent tree written for left clusters and we need to
split extent.
But we don't have enough metadata to accommodate the split extent records.
So extent tree need to grow.
BUG. no metadata is reserved ahead of time.
Thanks,
Changwei
>
> Thanks,
> Junxiao.
>>
>> 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.
>>
>> 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>
>> Reviewed-by: Duan Zhang <zhang.d...@h3c.com>
>> ---
>> fs/ocfs2/alloc.c | 140
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++---
>> fs/ocfs2/alloc.h | 1 +
>> fs/ocfs2/aops.c | 14 ++++--
>> 3 files changed, 145 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
>> index ab5105f..56aba96 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) {
>> @@ -6562,7 +6584,7 @@ int ocfs2_run_deallocs(struct ocfs2_super *osb,
>> static struct ocfs2_per_slot_free_list *
>> ocfs2_find_per_slot_free_list(int type,
>> int slot,
>> - struct ocfs2_cached_dealloc_ctxt *ctxt)
>> + struct ocfs2_cached_dealloc_ctxt *ctxt, int new)
>> {
>> struct ocfs2_per_slot_free_list *fl = ctxt->c_first_suballocator;
>>
>> @@ -6573,6 +6595,10 @@ ocfs2_find_per_slot_free_list(int type,
>> fl = fl->f_next_suballocator;
>> }
>>
>> + /* we didn't find any, just return NULL if _new_is not set. */
>> + if (!new)
>> + return NULL;
>> +
>> fl = kmalloc(sizeof(*fl), GFP_NOFS);
>> if (fl) {
>> fl->f_inode_type = type;
>> @@ -6585,6 +6611,106 @@ 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, 0);
>> +
>> + 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, 0);
>> + /* The caller should guarantee that dealloc has cached some
>> + * extent blocks.
>> + */
>> + BUG_ON(!fl);
>> +
>> + bf = fl->f_first;
>> + fl->f_first = bf->free_next;
>> +
>> + 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]);
>> +
>> + if (!fl->f_first) {
>> + dealloc->c_first_suballocator = fl->f_next_suballocator;
>> + 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)
>> @@ -6593,7 +6719,7 @@ int ocfs2_cache_block_dealloc(struct
>> ocfs2_cached_dealloc_ctxt *ctxt,
>> struct ocfs2_per_slot_free_list *fl;
>> struct ocfs2_cached_block_free *item;
>>
>> - fl = ocfs2_find_per_slot_free_list(type, slot, ctxt);
>> + fl = ocfs2_find_per_slot_free_list(type, slot, ctxt, 1);
>> if (fl == NULL) {
>> ret = -ENOMEM;
>> mlog_errno(ret);
>> 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,
>> &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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