RE: [f2fs-dev] [PATCH 2/3] f2fs: cover more area with nat_tree_lock

[Chao Yu <chao2.yu@samsung.com>]

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> Sent: Sunday, January 03, 2016 9:26 AM
> To: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 2/3] f2fs: cover more area with nat_tree_lock
> 
> There was a subtle bug on nat cache management which incurs wrong nid allocation
> or wrong block addresses when try_to_free_nats is triggered heavily.
> This patch enlarges the previous coverage of nat_tree_lock to avoid data race.

Have you figured out how this happen? I'm curious about this issue,
since still I can't reproduce it and find any clue by reviewing code
so far.

Thanks,

> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  fs/f2fs/node.c | 29 ++++++++++++-----------------
>  1 file changed, 12 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 669c44e..4dab09f 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -262,13 +262,11 @@ static void cache_nat_entry(struct f2fs_nm_info *nm_i, nid_t nid,
>  {
>  	struct nat_entry *e;
> 
> -	down_write(&nm_i->nat_tree_lock);
>  	e = __lookup_nat_cache(nm_i, nid);
>  	if (!e) {
>  		e = grab_nat_entry(nm_i, nid);
>  		node_info_from_raw_nat(&e->ni, ne);
>  	}
> -	up_write(&nm_i->nat_tree_lock);
>  }
> 
>  static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
> @@ -380,6 +378,8 @@ void get_node_info(struct f2fs_sb_info *sbi, nid_t nid, struct node_info
> *ni)
> 
>  	memset(&ne, 0, sizeof(struct f2fs_nat_entry));
> 
> +	down_write(&nm_i->nat_tree_lock);
> +
>  	/* Check current segment summary */
>  	mutex_lock(&curseg->curseg_mutex);
>  	i = lookup_journal_in_cursum(sum, NAT_JOURNAL, nid, 0);
> @@ -400,6 +400,7 @@ void get_node_info(struct f2fs_sb_info *sbi, nid_t nid, struct node_info
> *ni)
>  cache:
>  	/* cache nat entry */
>  	cache_nat_entry(NM_I(sbi), nid, &ne);
> +	up_write(&nm_i->nat_tree_lock);
>  }
> 
>  /*
> @@ -1459,13 +1460,10 @@ static int add_free_nid(struct f2fs_sb_info *sbi, nid_t nid, bool build)
> 
>  	if (build) {
>  		/* do not add allocated nids */
> -		down_read(&nm_i->nat_tree_lock);
>  		ne = __lookup_nat_cache(nm_i, nid);
> -		if (ne &&
> -			(!get_nat_flag(ne, IS_CHECKPOINTED) ||
> +		if (ne && (!get_nat_flag(ne, IS_CHECKPOINTED) ||
>  				nat_get_blkaddr(ne) != NULL_ADDR))
>  			allocated = true;
> -		up_read(&nm_i->nat_tree_lock);
>  		if (allocated)
>  			return 0;
>  	}
> @@ -1551,6 +1549,8 @@ static void build_free_nids(struct f2fs_sb_info *sbi)
>  	ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), FREE_NID_PAGES,
>  							META_NAT, true);
> 
> +	down_read(&nm_i->nat_tree_lock);
> +
>  	while (1) {
>  		struct page *page = get_current_nat_page(sbi, nid);
> 
> @@ -1579,6 +1579,7 @@ static void build_free_nids(struct f2fs_sb_info *sbi)
>  			remove_free_nid(nm_i, nid);
>  	}
>  	mutex_unlock(&curseg->curseg_mutex);
> +	up_read(&nm_i->nat_tree_lock);
> 
>  	ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nm_i->next_scan_nid),
>  					nm_i->ra_nid_pages, META_NAT, false);
> @@ -1861,14 +1862,12 @@ static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
> 
>  		raw_ne = nat_in_journal(sum, i);
> 
> -		down_write(&nm_i->nat_tree_lock);
>  		ne = __lookup_nat_cache(nm_i, nid);
>  		if (!ne) {
>  			ne = grab_nat_entry(nm_i, nid);
>  			node_info_from_raw_nat(&ne->ni, &raw_ne);
>  		}
>  		__set_nat_cache_dirty(nm_i, ne);
> -		up_write(&nm_i->nat_tree_lock);
>  	}
>  	update_nats_in_cursum(sum, -i);
>  	mutex_unlock(&curseg->curseg_mutex);
> @@ -1902,7 +1901,6 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
>  	struct f2fs_nat_block *nat_blk;
>  	struct nat_entry *ne, *cur;
>  	struct page *page = NULL;
> -	struct f2fs_nm_info *nm_i = NM_I(sbi);
> 
>  	/*
>  	 * there are two steps to flush nat entries:
> @@ -1939,12 +1937,8 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
>  			raw_ne = &nat_blk->entries[nid - start_nid];
>  		}
>  		raw_nat_from_node_info(raw_ne, &ne->ni);
> -
> -		down_write(&NM_I(sbi)->nat_tree_lock);
>  		nat_reset_flag(ne);
>  		__clear_nat_cache_dirty(NM_I(sbi), ne);
> -		up_write(&NM_I(sbi)->nat_tree_lock);
> -
>  		if (nat_get_blkaddr(ne) == NULL_ADDR)
>  			add_free_nid(sbi, nid, false);
>  	}
> @@ -1956,9 +1950,7 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> 
>  	f2fs_bug_on(sbi, set->entry_cnt);
> 
> -	down_write(&nm_i->nat_tree_lock);
>  	radix_tree_delete(&NM_I(sbi)->nat_set_root, set->set);
> -	up_write(&nm_i->nat_tree_lock);
>  	kmem_cache_free(nat_entry_set_slab, set);
>  }
> 
> @@ -1978,6 +1970,9 @@ void flush_nat_entries(struct f2fs_sb_info *sbi)
> 
>  	if (!nm_i->dirty_nat_cnt)
>  		return;
> +
> +	down_write(&nm_i->nat_tree_lock);
> +
>  	/*
>  	 * if there are no enough space in journal to store dirty nat
>  	 * entries, remove all entries from journal and merge them
> @@ -1986,7 +1981,6 @@ void flush_nat_entries(struct f2fs_sb_info *sbi)
>  	if (!__has_cursum_space(sum, nm_i->dirty_nat_cnt, NAT_JOURNAL))
>  		remove_nats_in_journal(sbi);
> 
> -	down_write(&nm_i->nat_tree_lock);
>  	while ((found = __gang_lookup_nat_set(nm_i,
>  					set_idx, SETVEC_SIZE, setvec))) {
>  		unsigned idx;
> @@ -1995,12 +1989,13 @@ void flush_nat_entries(struct f2fs_sb_info *sbi)
>  			__adjust_nat_entry_set(setvec[idx], &sets,
>  							MAX_NAT_JENTRIES(sum));
>  	}
> -	up_write(&nm_i->nat_tree_lock);
> 
>  	/* flush dirty nats in nat entry set */
>  	list_for_each_entry_safe(set, tmp, &sets, set_list)
>  		__flush_nat_entry_set(sbi, set);
> 
> +	up_write(&nm_i->nat_tree_lock);
> +
>  	f2fs_bug_on(sbi, nm_i->dirty_nat_cnt);
>  }
> 
> --
> 2.6.3
> 
> 
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