Re: [PATCH] fix crash on ocfs2_duplicate_clusters_by_page

[Andrew Morton]

On Wed, 29 Aug 2018 15:47:40 +0800 Larry Chen <lchen@xxxxxxxx> wrote:

> ocfs2_duplicate_clusters_by_page may crash if one of extent's pages is dirty.
> When a page has not been written back, it is still in dirty state. If 
> ocfs2_duplicate_clusters_by_page is called against the
> dirty page, the crash happens.
> 
> To fix this bug, we can just unlock the page and wait the page until
> it's not dirty.
> 
> The following is the buck trace dump:
> 
> kernel BUG at /root/code/ocfs2/refcounttree.c:2961!
> [exception RIP: ocfs2_duplicate_clusters_by_page+822]
> __ocfs2_move_extent+0x80/0x450 [ocfs2]
> ? __ocfs2_claim_clusters+0x130/0x250 [ocfs2]
> ocfs2_defrag_extent+0x5b8/0x5e0 [ocfs2]
> __ocfs2_move_extents_range+0x2a4/0x470 [ocfs2]
> ocfs2_move_extents+0x180/0x3b0 [ocfs2]
> ? ocfs2_wait_for_recovery+0x13/0x70 [ocfs2]
> ocfs2_ioctl_move_extents+0x133/0x2d0 [ocfs2]
> ocfs2_ioctl+0x253/0x640 [ocfs2]
> do_vfs_ioctl+0x90/0x5f0
> SyS_ioctl+0x74/0x80
> do_syscall_64+0x74/0x140
> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> 
> --- a/fs/ocfs2/refcounttree.c
> +++ b/fs/ocfs2/refcounttree.c
> @@ -2946,6 +2946,7 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
>  		if (map_end & (PAGE_SIZE - 1))
>  			to = map_end & (PAGE_SIZE - 1);
>  
> +retry:
>  		page = find_or_create_page(mapping, page_index, GFP_NOFS);
>  		if (!page) {
>  			ret = -ENOMEM;
> @@ -2957,8 +2958,15 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
>  		 * In case PAGE_SIZE <= CLUSTER_SIZE, This page
>  		 * can't be dirtied before we CoW it out.
>  		 */

Looks sane, but the below change shows that the above comment is
untrue.  Can we please update the comment as well?


> -		if (PAGE_SIZE <= OCFS2_SB(sb)->s_clustersize)
> -			BUG_ON(PageDirty(page));
> +		if (PAGE_SIZE <= OCFS2_SB(sb)->s_clustersize) {
> +			if (PageDirty(page)) {
> +				/*
> +				 * write_on_page will unlock the page on return
> +				 */
> +				ret = write_one_page(page);
> +				goto retry;
> +			}
> +		}
>  
>  		if (!PageUptodate(page)) {
>  			ret = block_read_full_page(page, ocfs2_get_block);