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SubjectRe: [f2fs-dev] [PATCH] f2fs: avoid race condition for shinker count
On 11/10, Chao Yu wrote:
> On 2020/11/10 12:19, Jaegeuk Kim wrote:
> > On 11/10, Chao Yu wrote:
> > > On 2020/11/10 1:00, Jaegeuk Kim wrote:
> > > > Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in
> > >
> > > I didn't get the problem clearly, did you mean __count_nat_entries() will
> > > give the wrong shrink count due to race condition? should there be a lock
> > > while reading these two variables?
> > >
> > > > wrong do_shinker work. Basically the two counts should not happen like that.
> > > >
> > > > So, I suspect this race condtion where:
> > > > - f2fs_try_to_free_nats __flush_nat_entry_set
> > > > nat_cnt=2, dirty_nat_cnt=2
> > > > __clear_nat_cache_dirty
> > > > spin_lock(nat_list_lock)
> > > > list_move()
> > > > spin_unlock(nat_list_lock)
> > > > spin_lock(nat_list_lock)
> > > > list_del()
> > > > spin_unlock(nat_list_lock)
> > > > nat_cnt=1, dirty_nat_cnt=2
> > > > nat_cnt=1, dirty_nat_cnt=1
> > >
> > > nm_i->nat_cnt and nm_i->dirty_nat_cnt were protected by
> > > nm_i->nat_tree_lock, I didn't see why expanding nat_list_lock range
> > > will help... since there are still places nat_list_lock() didn't
> > > cover these two reference counts.
> >
> > Yeah, I missed nat_tree_lock, and indeed it should cover this. So, the problem
> > is Light reported subtle case of nat_cnt < dirty_nat_cnt in shrink_count.
> > We may need to use nat_tree_lock in shrink_count?
>
> change like this?
>

Yup.

> __count_nat_entries()
>
> down_read(&nm_i->nat_tree_lock);
> count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
> up_read(&nm_i->nat_tree_lock);
>
> Thanks,
>
> >
> > >
> > > Thanks,
> > >
> > > >
> > > > Reported-by: Light Hsieh <Light.Hsieh@mediatek.com>
> > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > > > ---
> > > > fs/f2fs/node.c | 3 +--
> > > > 1 file changed, 1 insertion(+), 2 deletions(-)
> > > >
> > > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > > > index 42394de6c7eb..e8ec65e40f06 100644
> > > > --- a/fs/f2fs/node.c
> > > > +++ b/fs/f2fs/node.c
> > > > @@ -269,11 +269,10 @@ static void __clear_nat_cache_dirty(struct f2fs_nm_info *nm_i,
> > > > {
> > > > spin_lock(&nm_i->nat_list_lock);
> > > > list_move_tail(&ne->list, &nm_i->nat_entries);
> > > > - spin_unlock(&nm_i->nat_list_lock);
> > > > -
> > > > set_nat_flag(ne, IS_DIRTY, false);
> > > > set->entry_cnt--;
> > > > nm_i->dirty_nat_cnt--;
> > > > + spin_unlock(&nm_i->nat_list_lock);
> > > > }
> > > > static unsigned int __gang_lookup_nat_set(struct f2fs_nm_info *nm_i,
> > > >
> > .
> >

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