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@xxxxxxxxxx>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--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
>
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