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.hs...@mediatek.com>
> Signed-off-by: Jaegeuk Kim <jaeg...@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
Let me just check like this.
>From 971163330224449d90aac90957ea38f77d494f0f Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaeg...@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.hs...@mediatek.com>
Signed-off-by: Jaegeuk Kim <jaeg...@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;
+ return 0;
}
static unsigned long __count_free_nids(struct f2fs_sb_info *sbi)
--
2.29.2.454.gaff20da3a2-goog
>
> return count > 0 ? count : 0;
> }
> --
> 2.29.2.299.gdc1121823c-goog
>
>
>
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