Re: [f2fs-dev] [PATCH 1/5] f2fs: relax node version check for victim data in gc

[heyunlei]

Hi allï

On 2017/3/26 5:27, Jaegeuk Kim wrote:
> On 03/25, Chao Yu wrote:
> > Hi Jaegeuk,
> >
> > On 2017/3/25 15:59, Jaegeuk Kim wrote:
> > > - has_not_enough_free_secs
> > > node_secs: 0  dent_secs: 0  freed:0  free_segments:103  reserved:104
> > >
> > >           - f2fs_gc
> > >              - get_victim_by_default
> > > alloc_mode 0, gc_mode 1, max_search 2672, offset 4654, ofs_unit 1
> > >
> > >                 - do_garbage_collect
> > > start_segno 3976, end_segno 3977   type 0
> > >
> > >                   - is_alive
> > > nid 22797, blkaddr 2131882, ofs_in_node 0, version 0x8/0x0
> > >
> > >                    - gc_data_segment 766, segno 3976, block 512/426 not alive
> > >
> > > So, this patch fixes subtle corrupted case where node version does not match
> > > to summary version which results in infinite loop by gc.
> > >
> > > Reported-by: Yunlei He <heyunlei@xxxxxxxxxx>
> > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > ---
> > >  fs/f2fs/gc.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > > index 939be88a8833..bbeee41aaf73 100644
> > > --- a/fs/f2fs/gc.c
> > > +++ b/fs/f2fs/gc.c
> > > @@ -551,8 +551,10 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> > >  	get_node_info(sbi, nid, dni);
> > >
> > >  	if (sum->version != dni->version) {
> >
> > If the node was been truncated, we will increase its version number, since it
> > was been truncated, so it will never be writebacked to storage, so the version
> > in summary will not be updated.

The same problem I came across with a node segment:

481                 get_node_info(sbi, nid, &ni);
482                 if (ni.blk_addr != start_addr + off) {
483                         f2fs_put_page(node_page, 1);
484                         continue;
485                 }

Here, get victim method always selected segno 5169 for garbage collection,

but this section gc failed for upper condition:

	gc_node_segment 494, blk_addr 1697572,start_addr 2668544,off 200

I think is same problem with is_alive function.

Thanks.


> That's covered by node page lock, so we shouldn't be reached out to this point.
> Let's think more about this.
>
> Thanks,
>
> > So this case can happen, shouldn't we just set SBI_NEED_FSCK for the case:
> > sum->version != dni->version - 1
> >
> > Thanks,
> >
> > > -		f2fs_put_page(node_page, 1);
> > > -		return false;
> > > +		f2fs_msg(sbi->sb, KERN_WARNING,
> > > +				"%s: valid data with mismatched node version.",
> > > +				__func__);
> > > +		set_sbi_flag(sbi, SBI_NEED_FSCK);
> > >  	}
> > >
> > >  	*nofs = ofs_of_node(node_page);
>
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