Re: [PATCH v4] xfs: Fix deadlock between AGI and AGF when target_ip exists in xfs_rename()

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Nov 12, 2019 at 07:13:30PM +0800, kaixuxia wrote:
> When target_ip exists in xfs_rename(), the xfs_dir_replace() call may
> need to hold the AGF lock to allocate more blocks, and then invoking
> the xfs_droplink() call to hold AGI lock to drop target_ip onto the
> unlinked list, so we get the lock order AGF->AGI. This would break the
> ordering constraint on AGI and AGF locking - inode allocation locks
> the AGI, then can allocate a new extent for new inodes, locking the
> AGF after the AGI.
> 
> In this patch we check whether the replace operation need more
> blocks firstly. If so, acquire the agi lock firstly to preserve
> locking order(AGI/AGF). Actually, the locking order problem only
> occurs when we are locking the AGI/AGF of the same AG. For multiple
> AGs the AGI lock will be released after the transaction committed.
> 
> Signed-off-by: kaixuxia <kaixuxia@tencent.com>
> ---
> Changes in v4:
>  -Remove the typedef usages.
>  -Invoke xfs_dir2_sf_replace_needblock() in
>   xfs_dir2_sf_replace() directly.
> 
>  fs/xfs/libxfs/xfs_dir2.h    |  2 ++
>  fs/xfs/libxfs/xfs_dir2_sf.c | 28 +++++++++++++++++++++++-----
>  fs/xfs/xfs_inode.c          | 15 +++++++++++++++
>  3 files changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_dir2.h b/fs/xfs/libxfs/xfs_dir2.h
> index f542447..01b1722 100644
> --- a/fs/xfs/libxfs/xfs_dir2.h
> +++ b/fs/xfs/libxfs/xfs_dir2.h
> @@ -124,6 +124,8 @@ extern int xfs_dir_lookup(struct xfs_trans *tp, struct xfs_inode *dp,
>  extern int xfs_dir_removename(struct xfs_trans *tp, struct xfs_inode *dp,
>  				struct xfs_name *name, xfs_ino_t ino,
>  				xfs_extlen_t tot);
> +extern bool xfs_dir2_sf_replace_needblock(struct xfs_inode *dp,
> +				xfs_ino_t inum);
>  extern int xfs_dir_replace(struct xfs_trans *tp, struct xfs_inode *dp,
>  				struct xfs_name *name, xfs_ino_t inum,
>  				xfs_extlen_t tot);
> diff --git a/fs/xfs/libxfs/xfs_dir2_sf.c b/fs/xfs/libxfs/xfs_dir2_sf.c
> index 85f14fc..0e112e1 100644
> --- a/fs/xfs/libxfs/xfs_dir2_sf.c
> +++ b/fs/xfs/libxfs/xfs_dir2_sf.c
> @@ -945,6 +945,27 @@ static int xfs_dir2_sf_addname_pick(xfs_da_args_t *args, int objchange,
>  }
>  
>  /*
> + * Check whether the sf dir replace operation need more blocks.
> + */
> +bool
> +xfs_dir2_sf_replace_needblock(
> +	struct xfs_inode	*dp,
> +	xfs_ino_t		inum)
> +{
> +	int			newsize;
> +	struct xfs_dir2_sf_hdr	*sfp;
> +
> +	if (dp->i_d.di_format != XFS_DINODE_FMT_LOCAL)
> +		return false;
> +
> +	sfp = (struct xfs_dir2_sf_hdr *)dp->i_df.if_u1.if_data;
> +	newsize = dp->i_df.if_bytes + (sfp->count + 1) * XFS_INO64_DIFF;
> +
> +	return inum > XFS_DIR2_MAX_SHORT_INUM &&
> +	       sfp->i8count == 0 && newsize > XFS_IFORK_DSIZE(dp);
> +}
> +
> +/*
>   * Replace the inode number of an entry in a shortform directory.
>   */
>  int						/* error */
> @@ -980,17 +1001,14 @@ static int xfs_dir2_sf_addname_pick(xfs_da_args_t *args, int objchange,
>  	 */
>  	if (args->inumber > XFS_DIR2_MAX_SHORT_INUM && sfp->i8count == 0) {
>  		int	error;			/* error return value */
> -		int	newsize;		/* new inode size */
>  
> -		newsize = dp->i_df.if_bytes + (sfp->count + 1) * XFS_INO64_DIFF;
>  		/*
>  		 * Won't fit as shortform, convert to block then do replace.
>  		 */
> -		if (newsize > XFS_IFORK_DSIZE(dp)) {
> +		if (xfs_dir2_sf_replace_needblock(dp, args->inumber)) {
>  			error = xfs_dir2_sf_to_block(args);
> -			if (error) {
> +			if (error)
>  				return error;
> -			}
>  			return xfs_dir2_block_replace(args);
>  		}
>  		/*
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 18f4b26..5dc3796 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -3196,6 +3196,7 @@ struct xfs_iunlink {
>  	struct xfs_trans	*tp;
>  	struct xfs_inode	*wip = NULL;		/* whiteout inode */
>  	struct xfs_inode	*inodes[__XFS_SORT_INODES];
> +	struct xfs_buf		*agibp;
>  	int			num_inodes = __XFS_SORT_INODES;
>  	bool			new_parent = (src_dp != target_dp);
>  	bool			src_is_directory = S_ISDIR(VFS_I(src_ip)->i_mode);
> @@ -3361,6 +3362,20 @@ struct xfs_iunlink {
>  		 * In case there is already an entry with the same
>  		 * name at the destination directory, remove it first.
>  		 */
> +
> +		/*
> +		 * Check whether the replace operation need more blocks.
> +		 * If so, acquire the agi lock firstly to preserve locking
> +		 * order (AGI/AGF). Only convert the shortform directory to
> +		 * block form maybe need more blocks.

The comment still seems a little clunky.  How about:

"Check whether the replace operation will need to allocate blocks.  This
happens when the shortform directory lacks space and we have to convert
it to a block format directory.  When more blocks are necessary we must
lock the AGI first to preserve locking order (AGI -> AGF)."

> +		 */
> +		if (xfs_dir2_sf_replace_needblock(target_dp, src_ip->i_ino)) {
> +			error = xfs_read_agi(mp, tp,
> +				XFS_INO_TO_AGNO(mp, target_ip->i_ino), &agibp);

The second line needs a double indent.

I can fix both of these on commit if Brian doesn't have any further
suggestions.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> +			if (error)
> +				goto out_trans_cancel;
> +		}
> +
>  		error = xfs_dir_replace(tp, target_dp, target_name,
>  					src_ip->i_ino, spaceres);
>  		if (error)
> -- 
> 1.8.3.1
>