lkml.org 
[lkml]   [2020]   [Nov]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [f2fs-dev] [PATCH] f2fs: avoid race condition for shinker count
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?

>
> 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,
> >

\
 
 \ /
  Last update: 2020-11-10 05:21    [W:1.024 / U:0.044 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site