Re: [Ocfs2-devel] [PATCH] fix crash on ocfs2_duplicate_clusters_by_page

[Changwei Ge]

Hi Larry,

Besides Andrew's comments, other parts of this patch look good to me.

Thanks,

Changwei


On 2018/8/30 6:25, Andrew Morton wrote:
> 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);
>
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