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

[Changwei Ge]

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,
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 (clusters_to_add == 0)
  		goto out;
  
-- 
2.7.4