Messages in this thread | | | Date | Wed, 11 Nov 2020 21:31:22 -0800 | From | Jaegeuk Kim <> | Subject | Re: [f2fs-dev] [PATCH] f2fs: avoid race condition for shinker count |
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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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