From 2192b0baea395274ffcd38ec70e284389e3c243d Mon Sep 17 00:00:00 2001
From: Brian Foster <bfoster@redhat.com>
Date: Wed, 5 Jul 2017 12:07:52 -0700
Subject: [PATCH] xfs: fix contiguous dquot chunk iteration livelock
Git-commit: 2192b0baea395274ffcd38ec70e284389e3c243d
Patch-mainline: v4.13-rc1
References: bsc#1070995

The patch below updated xfs_dq_get_next_id() to use the XFS iext
lookup helpers to locate the next quota id rather than to seek for
data in the quota file. The updated code fails to correctly handle
the case where the quota inode might have contiguous chunks part of
the same extent. In this case, the start block offset is calculated
based on the next expected id but the extent lookup returns the same
start offset as for the previous chunk. This causes the returned id
to go backwards and livelocks the quota iteration. This problem is
reproduced intermittently by generic/232.

To handle this case, check whether the startoff from the extent
lookup is behind the startoff calculated from the next quota id. If
so, bump up got.br_startoff to the specific file offset that is
expected to hold the next dquot chunk.

Fixes: bda250dbaf39 ("xfs: rewrite xfs_dq_get_next_id using xfs_iext_lookup_extent")
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Anthony Iliopoulos <ailiopoulos@suse.com>

---
 fs/xfs/xfs_dquot.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
index 8848b397e7a8..f89f7b5241e6 100644
--- a/fs/xfs/xfs_dquot.c
+++ b/fs/xfs/xfs_dquot.c
@@ -733,10 +733,15 @@ xfs_dq_get_next_id(
 			return error;
 	}
 
-	if (xfs_iext_lookup_extent(quotip, &quotip->i_df, start, &idx, &got))
+	if (xfs_iext_lookup_extent(quotip, &quotip->i_df, start, &idx, &got)) {
+		/* contiguous chunk, bump startoff for the id calculation */
+		if (got.br_startoff < start)
+			got.br_startoff = start;
 		*id = got.br_startoff * mp->m_quotainfo->qi_dqperchunk;
-	else
+	} else {
 		error = -ENOENT;
+	}
+
 	xfs_iunlock(quotip, lock_flags);
 
 	return error;
-- 
2.16.4