Hi John,
It's better to paste your patch directly into message body. It's easy
for reviewing.
So I copied your patch below:
> The dw_zero_count tracking was assuming that w_unwritten_list would
> always contain one element. The actual count is now tracked whenever
> the list is extended.
> ---
> fs/ocfs2/aops.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index 88a31e9340a0..eb0a81368dbb 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c
> @@ -784,6 +784,8 @@ 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)
> @@ -873,6 +875,7 @@ static int ocfs2_alloc_write_ctxt(struct ocfs2_write_ctxt
> **wcp,
>
> ocfs2_init_dealloc_ctxt(&wc->w_dealloc);
> INIT_LIST_HEAD(&wc->w_unwritten_list);
> + wc->w_unwritten_count = 0;
I think you don't have to evaluate ::w_unwritten_count to zero since
kzalloc already did that.
>
> *wcp = wc;
>
> @@ -1373,6 +1376,7 @@ 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++;
You increase ::w_unwritten_coun once a new _ue_ is attached to
::w_unwritten_list. So if no _ue_ ever is attached, ::w_unwritten_list
is still empty. I think your change has the same effect with origin.
Moreover I don't see the relation between the reported crash issue and
your patch change. Can you elaborate further?
Thanks,
Changwei
> new = NULL;
> unlock:
> spin_unlock(&oi->ip_lock);
> @@ -2246,7 +2250,7 @@ static int ocfs2_dio_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);
> --
> 2.11.0
On 2017/11/21 2:56, John Lightsey wrote:
> In January Ben Hutchings reported Debian bug 841144 to the ocfs2-devel
> list:
>
> https://oss.oracle.com/pipermail/ocfs2-devel/2017-January/012701.html
>
> cPanel encountered this bug after upgrading our cluster to the 4.9
> Debian stable kernel. In our environment, the bug would trigger every
> few hours.
>
> The core problem seems to be that the size of dw_zero_list is not
> tracked correctly. This causes the ocfs2_lock_allocators() call in
> ocfs2_dio_end_io_write() to underestimate the number of extents needed.
> As a result, meta_ac is null when it's needed in ocfs2_grow_tree().
>
> The attached patch is a forward-ported version of the fix we applied to
> Debian's 4.9 kernel to correct the issue.
>
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