Re: [PATCH] fix crash on ocfs2_duplicate_clusters_by_page

From: Andrew Morton
Date: Wed Aug 29 2018 - 18:25:38 EST


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);