Re: [PATCH 02/11] xfs: create the XFS_QMOPT_QUOTIP_LOCKED flag

[Brian Foster <bfoster@redhat.com>]

On Tue, Apr 17, 2018 at 07:39:39PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Create a new QMOPT flag to signal that we've already locked the quota
> inode.  This will be used by the quota scrub code refactoring to avoid
> dropping the quota ip lock during scrub.  The flag is incompatible with
> the DQALLOC flag because dquot allocation creates a transaction, and we
> shouldn't be doing that with the ILOCK held.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_quota_defs.h |    2 ++
>  fs/xfs/xfs_dquot.c             |   32 ++++++++++++++++++++------------
>  2 files changed, 22 insertions(+), 12 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_quota_defs.h b/fs/xfs/libxfs/xfs_quota_defs.h
> index bb1b13a..cfc9938 100644
> --- a/fs/xfs/libxfs/xfs_quota_defs.h
> +++ b/fs/xfs/libxfs/xfs_quota_defs.h
> @@ -107,6 +107,8 @@ typedef uint16_t	xfs_qwarncnt_t;
>   * to a single function. None of these XFS_QMOPT_* flags are meant to have
>   * persistent values (ie. their values can and will change between versions)
>   */
> +/* Quota ip already locked.  Cannot be used with DQALLOC. */
> +#define XFS_QMOPT_QUOTIP_LOCKED	0x0000001
>  #define XFS_QMOPT_DQALLOC	0x0000002 /* alloc dquot ondisk if needed */
>  #define XFS_QMOPT_UQUOTA	0x0000004 /* user dquot requested */
>  #define XFS_QMOPT_PQUOTA	0x0000008 /* project dquot requested */
> diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> index a7daef9..ed2e37c 100644
> --- a/fs/xfs/xfs_dquot.c
> +++ b/fs/xfs/xfs_dquot.c
> @@ -417,18 +417,20 @@ xfs_qm_dqtobp(
>  	struct xfs_mount	*mp = dqp->q_mount;
>  	xfs_dqid_t		id = be32_to_cpu(dqp->q_core.d_id);
>  	struct xfs_trans	*tp = (tpp ? *tpp : NULL);
> -	uint			lock_mode;
> +	uint			lock_mode = 0;
>  
>  	quotip = xfs_quota_inode(dqp->q_mount, dqp->dq_flags);
>  	dqp->q_fileoffset = (xfs_fileoff_t)id / mp->m_quotainfo->qi_dqperchunk;
>  
> -	lock_mode = xfs_ilock_data_map_shared(quotip);
> +	if (!(flags & XFS_QMOPT_QUOTIP_LOCKED))
> +		lock_mode = xfs_ilock_data_map_shared(quotip);
>  	if (!xfs_this_quota_on(dqp->q_mount, dqp->dq_flags)) {
>  		/*
>  		 * Return if this type of quotas is turned off while we
>  		 * didn't have the quota inode lock.
>  		 */
> -		xfs_iunlock(quotip, lock_mode);
> +		if (lock_mode)
> +			xfs_iunlock(quotip, lock_mode);
>  		return -ESRCH;
>  	}
>  
> @@ -438,7 +440,8 @@ xfs_qm_dqtobp(
>  	error = xfs_bmapi_read(quotip, dqp->q_fileoffset,
>  			       XFS_DQUOT_CLUSTER_SIZE_FSB, &map, &nmaps, 0);
>  
> -	xfs_iunlock(quotip, lock_mode);
> +	if (lock_mode)
> +		xfs_iunlock(quotip, lock_mode);
>  	if (error)
>  		return error;
>  
> @@ -458,7 +461,7 @@ xfs_qm_dqtobp(
>  		 */
>  		if (!(flags & XFS_QMOPT_DQALLOC))
>  			return -ENOENT;
> -
> +		ASSERT(!(flags & XFS_QMOPT_QUOTIP_LOCKED));
>  		ASSERT(tp);
>  		error = xfs_qm_dqalloc(tpp, mp, dqp, quotip,
>  					dqp->q_fileoffset, &bp);
> @@ -553,6 +556,7 @@ xfs_qm_dqread(
>  	trace_xfs_dqread(dqp);
>  
>  	if (flags & XFS_QMOPT_DQALLOC) {
> +		ASSERT(!(flags & XFS_QMOPT_QUOTIP_LOCKED));

Perhaps we should just have an explicit check for both flags above and
return with -EINVAL if necessary?

>  		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_qm_dqalloc,
>  				XFS_QM_DQALLOC_SPACE_RES(mp), 0, 0, &tp);
>  		if (error)
> @@ -634,11 +638,12 @@ static int
>  xfs_dq_get_next_id(
>  	struct xfs_mount	*mp,
>  	uint			type,
> -	xfs_dqid_t		*id)
> +	xfs_dqid_t		*id,
> +	uint			flags)
>  {
>  	struct xfs_inode	*quotip = xfs_quota_inode(mp, type);
>  	xfs_dqid_t		next_id = *id + 1; /* simple advance */
> -	uint			lock_flags;
> +	uint			lock_flags = 0;
>  	struct xfs_bmbt_irec	got;
>  	struct xfs_iext_cursor	cur;
>  	xfs_fsblock_t		start;
> @@ -657,7 +662,8 @@ xfs_dq_get_next_id(
>  	/* Nope, next_id is now past the current chunk, so find the next one */
>  	start = (xfs_fsblock_t)next_id / mp->m_quotainfo->qi_dqperchunk;
>  
> -	lock_flags = xfs_ilock_data_map_shared(quotip);
> +	if (!(flags & XFS_QMOPT_QUOTIP_LOCKED))
> +		lock_flags = xfs_ilock_data_map_shared(quotip);
>  	if (!(quotip->i_df.if_flags & XFS_IFEXTENTS)) {
>  		error = xfs_iread_extents(NULL, quotip, XFS_DATA_FORK);
>  		if (error)
> @@ -673,7 +679,8 @@ xfs_dq_get_next_id(
>  		error = -ENOENT;
>  	}
>  
> -	xfs_iunlock(quotip, lock_flags);
> +	if (lock_flags)
> +		xfs_iunlock(quotip, lock_flags);
>  
>  	return error;
>  }
> @@ -733,7 +740,8 @@ xfs_qm_dqget(

Earlier code in this function drops/reacquires the ip ILOCK with a note
in the comment around lock ordering with the quota inode. Assuming an
inode is passed, is that lock cycle safe if the caller also has the
quotip held locked?

Brian

>  			if (XFS_IS_DQUOT_UNINITIALIZED(dqp)) {
>  				xfs_dqunlock(dqp);
>  				mutex_unlock(&qi->qi_tree_lock);
> -				error = xfs_dq_get_next_id(mp, type, &id);
> +				error = xfs_dq_get_next_id(mp, type, &id,
> +						flags);
>  				if (error)
>  					return error;
>  				goto restart;
> @@ -768,7 +776,7 @@ xfs_qm_dqget(
>  
>  	/* If we are asked to find next active id, keep looking */
>  	if (error == -ENOENT && (flags & XFS_QMOPT_DQNEXT)) {
> -		error = xfs_dq_get_next_id(mp, type, &id);
> +		error = xfs_dq_get_next_id(mp, type, &id, flags);
>  		if (!error)
>  			goto restart;
>  	}
> @@ -827,7 +835,7 @@ xfs_qm_dqget(
>  	if (flags & XFS_QMOPT_DQNEXT) {
>  		if (XFS_IS_DQUOT_UNINITIALIZED(dqp)) {
>  			xfs_qm_dqput(dqp);
> -			error = xfs_dq_get_next_id(mp, type, &id);
> +			error = xfs_dq_get_next_id(mp, type, &id, flags);
>  			if (error)
>  				return error;
>  			goto restart;
> 
> --
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