Re: [PATCHv5 10/16] exofs: fix race condition in marking SB dirty

[Boaz Harrosh]

On 06/06/2010 05:50 PM, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
> 
> When synchronizing the superblock, exofs first initiates the SB write
> (a) and then marks the superblock as clean (b). However, meanwhile
> (between (a) and (b)) someone else can modify the superblock and
> mark it as dirty. This would be a race condition, and the result
> would be that we'd end up with a modified superblock which would
> nevertheless be marked as clean (because of (b)). This means that
> 'sync_supers()' would never call our '->write_super()', at least
> not until yet another SB change happens.
> 
> This patch fixes this race condition by marking the superblock as
> clean before initiating the write operation.
> 
> Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
> Cc: Boaz Harrosh <bharrosh@xxxxxxxxxxx>

Ack-by: Boaz Harrosh <bharrosh@xxxxxxxxxxx>

Grate fix thanks
Boaz

> ---
>  fs/exofs/super.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/exofs/super.c b/fs/exofs/super.c
> index 74ccbdc..0b432b9 100644
> --- a/fs/exofs/super.c
> +++ b/fs/exofs/super.c
> @@ -219,6 +219,7 @@ int exofs_sync_fs(struct super_block *sb, int wait)
>  	 *       the fscb->s_dev_table_oid member. There is no read-modify-write
>  	 *       here.
>  	 */
> +	sb_mark_clean(sb);
>  	ios->length = offsetof(struct exofs_fscb, s_dev_table_oid);
>  	memset(fscb, 0, ios->length);
>  	fscb->s_nextid = cpu_to_le64(sbi->s_nextid);
> @@ -237,7 +238,6 @@ int exofs_sync_fs(struct super_block *sb, int wait)
>  		EXOFS_ERR("%s: exofs_sbi_write failed.\n", __func__);
>  		goto out;
>  	}
> -	sb_mark_clean(sb);
>  
>  out:
>  	EXOFS_DBGMSG("s_nextid=0x%llx ret=%d\n", _LLU(sbi->s_nextid), ret);

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