Re: [PATCH] f2fs: fix wrong sum_page pointer in f2fs_gc

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Fri, Oct 14, 2016 at 09:25:59PM +0800, Chao Yu wrote:
> On 2016/10/14 1:14, Jaegeuk Kim wrote:
> > On Thu, Oct 13, 2016 at 06:33:19PM +0800, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2016/10/13 7:23, Jaegeuk Kim wrote:
> >>> This patch fixes using a wrong pointer for sum_page in f2fs_gc.
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> >>> ---
> >>>  fs/f2fs/gc.c | 10 +++++-----
> >>>  1 file changed, 5 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index e48142f..9c18917 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -854,16 +854,16 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >>>  
> >>>  	for (segno = start_segno; segno < end_segno; segno++) {
> >>>  
> >>> -		if (get_valid_blocks(sbi, segno, 1) == 0 ||
> >>> -					unlikely(f2fs_cp_error(sbi)))
> >>> -			goto next;
> >>> -
> >>>  		/* find segment summary of victim */
> >>>  		sum_page = find_get_page(META_MAPPING(sbi),
> >>>  					GET_SUM_BLOCK(sbi, segno));
> >>> -		f2fs_bug_on(sbi, !PageUptodate(sum_page));
> >>>  		f2fs_put_page(sum_page, 0);
> >>>  
> >>> +		if (get_valid_blocks(sbi, segno, 1) == 0 ||
> >>> +				!PageUptodate(sum_page) ||
> >>
> >> Why uptodate flag of summary page can be cleared? someone truncates it?
> > 
> > Well, it looks like no problem to remove this, since it will hit
> > f2fs_cp_error(). I just intended to handle the above f2fs_bug_on here.
> 
> If summary page becomes non-uptodate, it seems there is a bug in vfs/mm/f2fs,
> why not keep it there to detect bug?

I found that the above get_sum_page() loop can give a page which is not uptodate
caused by EIO. Then, we would get the above bug_on, if we move f2fs_cp_error()
case like this patch.

Thoughts?

Thanks,

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