linux-ext4 - Re: [PATCH 1/5] ext4: fix race with setting free_inode/clusters

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Message-Id: <928E1D00-08F4-4ED9-987D-C9D6EDCD60CD@dilger.ca>
Date:   Mon, 4 Jun 2018 12:00:45 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Wang Shilong <wangshilong1991@...il.com>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Shuichi Ihara <sihara@....com>, Wang Shilong <wshilong@....com>
Subject: Re: [PATCH 1/5] ext4: fix race with setting
 free_inode/clusters_counter

On May 29, 2018, at 5:45 AM, Wang Shilong <wangshilong1991@...il.com> wrote:
> 
> From: Wang Shilong <wshilong@....com>
> 
> Whenever we hit block or inode bitmap corruptions we set
> bit and then reduce this block group free inode/clusters
> counter to expose right available space.
> 
> However some of ext4_mark_group_bitmap_corrupted() is called
> inside group spinlock, some are not, this could make it happen
> that we double reduce one block group free counters from system.
> 
> Always hold group spinlock for it could fix it, but it looks
> a little heavy, we could use test_and_set_bit() to fix race
> problems here.
> 
> Signed-off-by: Wang Shilong <wshilong@....com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> fs/ext4/super.c | 22 +++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index c1c5c87..d6fa6cf 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -770,26 +770,26 @@ void ext4_mark_group_bitmap_corrupted(struct super_block *sb,
> 	struct ext4_sb_info *sbi = EXT4_SB(sb);
> 	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
> 	struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL);
> +	int ret;
> 
> -	if ((flags & EXT4_GROUP_INFO_BBITMAP_CORRUPT) &&
> -	    !EXT4_MB_GRP_BBITMAP_CORRUPT(grp)) {
> -		percpu_counter_sub(&sbi->s_freeclusters_counter,
> -					grp->bb_free);
> -		set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT,
> -			&grp->bb_state);
> +	if (flags & EXT4_GROUP_INFO_BBITMAP_CORRUPT) {
> +		ret = ext4_test_and_set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT,
> +					    &grp->bb_state);
> +		if (!ret)
> +			percpu_counter_sub(&sbi->s_freeclusters_counter,
> +					   grp->bb_free);
> 	}
> 
> -	if ((flags & EXT4_GROUP_INFO_IBITMAP_CORRUPT) &&
> -	    !EXT4_MB_GRP_IBITMAP_CORRUPT(grp)) {
> -		if (gdp) {
> +	if (flags & EXT4_GROUP_INFO_IBITMAP_CORRUPT) {
> +		ret = ext4_test_and_set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT,
> +					    &grp->bb_state);
> +		if (!ret && gdp) {
> 			int count;
> 
> 			count = ext4_free_inodes_count(sb, gdp);
> 			percpu_counter_sub(&sbi->s_freeinodes_counter,
> 					   count);
> 		}
> -		set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT,
> -			&grp->bb_state);
> 	}
> }
> 
> --
> 1.8.3.1
> 


Cheers, Andreas






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