Messages in this thread | | | Subject | Re: [f2fs-dev] [PATCH v3] f2fs: avoid race condition for shinker count | From | Chao Yu <> | Date | Thu, 3 Dec 2020 14:55:50 +0800 |
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On 2020/12/3 14:07, Jaegeuk Kim wrote: > On 11/11, Jaegeuk Kim wrote: >> Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in >> wrong do_shinker work. Let's avoid to get stale data by using nat_tree_lock. >> >> Reported-by: Light Hsieh <Light.Hsieh@mediatek.com> >> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> >> --- >> v3: >> - fix to use NM_I(sbi) >> >> fs/f2fs/shrinker.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/fs/f2fs/shrinker.c b/fs/f2fs/shrinker.c >> index d66de5999a26..555712ba06d8 100644 >> --- a/fs/f2fs/shrinker.c >> +++ b/fs/f2fs/shrinker.c >> @@ -18,7 +18,11 @@ static unsigned int shrinker_run_no; >> >> static unsigned long __count_nat_entries(struct f2fs_sb_info *sbi) >> { >> - long count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt; >> + long count; >> + >> + down_read(&NM_I(sbi)->nat_tree_lock); >> + count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt; >> + up_read(&NM_I(sbi)->nat_tree_lock); > > I just fosund this can give kernel hang due to the following backtrace. > f2fs_shrink_count > shrink_slab > shrink_node > do_try_to_free_pages > try_to_free_pages > __alloc_pages_nodemask > alloc_pages_current > allocate_slab > __slab_alloc > __slab_alloc > kmem_cache_alloc > add_free_nid > f2fs_flush_nat_entries > f2fs_write_checkpoint
Oh, I missed that case.
> > Let me just check like this. > >>From 971163330224449d90aac90957ea38f77d494f0f Mon Sep 17 00:00:00 2001 > From: Jaegeuk Kim <jaegeuk@kernel.org> > Date: Fri, 6 Nov 2020 13:22:05 -0800 > Subject: [PATCH] f2fs: avoid race condition for shrinker count > > Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in > wrong do_shinker work. Let's avoid to return insane overflowed value. > > Reported-by: Light Hsieh <Light.Hsieh@mediatek.com> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > --- > fs/f2fs/shrinker.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/f2fs/shrinker.c b/fs/f2fs/shrinker.c > index d66de5999a26..75b5b4aaed99 100644 > --- a/fs/f2fs/shrinker.c > +++ b/fs/f2fs/shrinker.c > @@ -18,9 +18,9 @@ static unsigned int shrinker_run_no; > > static unsigned long __count_nat_entries(struct f2fs_sb_info *sbi) > { > - long count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt; > - > - return count > 0 ? count : 0; > + if (NM_I(sbi)->nat_cnt > NM_I(sbi)->dirty_nat_cnt) > + return NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
Hmm.. in the case that we are not in checkpoint progress, nat_cnt and dirty_nat_cnt is mutable, how can we make sure the calculation is non-negative after the check condition? :(
Thanks
> + return 0; > } > > static unsigned long __count_free_nids(struct f2fs_sb_info *sbi) >
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