Messages in this thread | | | Subject | Re: [f2fs-dev] [PATCH] f2fs: avoid race condition for shinker count | From | Chao Yu <> | Date | Tue, 10 Nov 2020 14:04:22 +0800 |
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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?
__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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