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

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Sun, Oct 23, 2016 at 08:26:15PM +0800, Chao Yu wrote:
> On 2016/10/15 0:57, Jaegeuk Kim wrote:
> > 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?
> 
> Seems this patch has already been merged into linus' tree...

Yup.

> Anyway, I can understand why you remove f2fs_bug_on & add PageUptodate here, but
> why should we repositon below check?
> 
> if (get_valid_blocks(sbi, segno, 1) == 0 ||
> 		unlikely(f2fs_cp_error(sbi)))

Given description, this fixes using wrong sum_page pointer by:

next:
	f2fs_put_page(sum_page, 0);

Thanks,

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