Re: [PATCH 5/5] xfs: wait on new inodes during quotaoff dquot release

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

On Wed, Feb 15, 2017 at 10:40:47AM -0500, Brian Foster wrote:
> The quotaoff operation has a race with inode allocation that results
> in a livelock. An inode allocation that occurs before the quota
> status flags are updated acquires the appropriate dquots for the
> inode via xfs_qm_vop_dqalloc(). It then inserts the XFS_INEW inode
> into the perag radix tree, sometime later attaches the dquots to the
> inode and finally clears the XFS_INEW flag. Quotaoff expects to
> release the dquots from all inodes in the filesystem via
> xfs_qm_dqrele_all_inodes(). This invokes the AG inode iterator,
> which skips inodes in the XFS_INEW state because they are not fully
> constructed. If the scan occurs after dquots have been attached to
> an inode, but before XFS_INEW is cleared, the newly allocated inode
> will continue to hold a reference to the applicable dquots. When
> quotaoff invokes xfs_qm_dqpurge_all(), the reference count of those
> dquot(s) remain elevated and the dqpurge scan spins indefinitely.
> 
> To address this problem, update the xfs_qm_dqrele_all_inodes() scan
> to wait on inodes marked on the XFS_INEW state. We wait on the
> inodes explicitly rather than skip and retry to avoid continuous
> retry loops due to a parallel inode allocation workload. Since
> quotaoff updates the quota state flags and uses a synchronous
> transaction before the dqrele scan, and dquots are attached to
> inodes after radix tree insertion iff quota is enabled, one INEW
> waiting pass through the AG guarantees that the scan has processed
> all inodes that could possibly hold dquot references.
> 
> Reported-by: Eryu Guan <eguan@redhat.com>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

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

--D

> ---
>  fs/xfs/xfs_qm_syscalls.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_qm_syscalls.c b/fs/xfs/xfs_qm_syscalls.c
> index dbb6802..40b7c3f 100644
> --- a/fs/xfs/xfs_qm_syscalls.c
> +++ b/fs/xfs/xfs_qm_syscalls.c
> @@ -765,5 +765,6 @@ xfs_qm_dqrele_all_inodes(
>  	uint		 flags)
>  {
>  	ASSERT(mp->m_quotainfo);
> -	xfs_inode_ag_iterator(mp, xfs_dqrele_inode, flags, NULL);
> +	xfs_inode_ag_iterator_flags(mp, xfs_dqrele_inode, flags, NULL,
> +				    XFS_AGITER_INEW_WAIT);
>  }
> -- 
> 2.7.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html