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Date:   Thu, 30 Aug 2018 07:43:44 +0000
From:   Changwei Ge <gechangwei@...e.cn>
To:     Larry Chen <lchen@...e.com>, "mark@...heh.com" <mark@...heh.com>,
        "jlbec@...lplan.org" <jlbec@...lplan.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH v4] fix crash on
 ocfs2_duplicate_clusters_by_page

Hi Larry,

Did you forget to add prefix 'ocfs2: ' to your patch title line?


On 2018/8/30 11:06, Larry Chen 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 write back the page rather than just wait.
>
> The following is the back trace dump:
>
> kernel BUG at /root/code/ocfs2/refcounttree.c:2961!
> 	BUG_ON(PageDirty(page));
> [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
>
>
> Change-log:
> 1. Once we find the page is dirty, we do not wait until it's clean,
>     but rather we use write_one_page to write it back
>
> 2. write_one_page arguments list changed, adjust and retest this patch.
>
> 3. Comments has been changed
>
>
> Signed-off-by: Larry Chen <lchen@...e.com>
> ---
>   fs/ocfs2/refcounttree.c | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
> index 7869622af22a..ed84d05c7d00 100644
> --- 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;
> @@ -2954,11 +2955,18 @@ 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.
> +		 * In case PAGE_SIZE <= CLUSTER_SIZE, we do not expect a dirty page,
> +		 * so write it back.
>   		 */
> -		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);

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