[PATCH] XFS: Account for allocated blocks when expanding directories

[Dave Chinner <david@fromorbit.com>]

When we create a directory, we reserve a number of blocks for
the maximum possible expansion of of the directory due to
various btree splits, freespace allocation, etc. Unfortunately,
each allocation is not reflected in the total number of blocks
still available to the transaction, so the maximal reservation
is used over and over again.

This leads to problems where an allocation group has only
enough blocks for *some* of the allocations required for the
directory modification. After the first N allocations, the
remaining blocks in the allocation group drops below the total
reservation, and subsequent allocations fail because the allocator
will not allow the allocation to proceed if the AG does not have
the enough blocks available for the entire allocation total.

This results in an ENOSPC occurring after an allocation has
already occurred. This results in aborting the directory
operation (leaving the directory in an inconsistent state)
and cancelling a dirty transaction, which results in a filesystem
shutdown.

Avoid the problem by reflecting the number of blocks allocated in
any directory expansion in the total number of blocks available to
the modification in progress. This prevents a directory modification
from being aborted part way through with an ENOSPC.

Signed-off-by: Dave Chinner <david@fromorbit.com>
---
 fs/xfs/xfs_da_btree.c |    5 +++++
 fs/xfs/xfs_dir2.c     |    6 ++++++
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_da_btree.c b/fs/xfs/xfs_da_btree.c
index 9e561a9..a11a839 100644
--- a/fs/xfs/xfs_da_btree.c
+++ b/fs/xfs/xfs_da_btree.c
@@ -1566,11 +1566,14 @@ xfs_da_grow_inode(xfs_da_args_t *args, xfs_dablk_t *new_blkno)
 	int nmap, error, w, count, c, got, i, mapi;
 	xfs_trans_t *tp;
 	xfs_mount_t *mp;
+	xfs_drfsbno_t	nblks;
 
 	dp = args->dp;
 	mp = dp->i_mount;
 	w = args->whichfork;
 	tp = args->trans;
+	nblks = dp->i_d.di_nblocks;
+
 	/*
 	 * For new directories adjust the file offset and block count.
 	 */
@@ -1647,6 +1650,8 @@ xfs_da_grow_inode(xfs_da_args_t *args, xfs_dablk_t *new_blkno)
 	}
 	if (mapp != &map)
 		kmem_free(mapp);
+	/* account for newly allocated blocks in reserved blocks total */
+	args->total -= dp->i_d.di_nblocks - nblks;
 	*new_blkno = (xfs_dablk_t)bno;
 	return 0;
 }
diff --git a/fs/xfs/xfs_dir2.c b/fs/xfs/xfs_dir2.c
index 80e0dc5..1afb122 100644
--- a/fs/xfs/xfs_dir2.c
+++ b/fs/xfs/xfs_dir2.c
@@ -525,11 +525,13 @@ xfs_dir2_grow_inode(
 	xfs_mount_t	*mp;
 	int		nmap;		/* number of bmap entries */
 	xfs_trans_t	*tp;
+	xfs_drfsbno_t	nblks;
 
 	xfs_dir2_trace_args_s("grow_inode", args, space);
 	dp = args->dp;
 	tp = args->trans;
 	mp = dp->i_mount;
+	nblks = dp->i_d.di_nblocks;
 	/*
 	 * Set lowest possible block in the space requested.
 	 */
@@ -622,7 +624,11 @@ xfs_dir2_grow_inode(
 	 */
 	if (mapp != &map)
 		kmem_free(mapp);
+
+	/* account for newly allocated blocks in reserved blocks total */
+	args->total -= dp->i_d.di_nblocks - nblks;
 	*dbp = xfs_dir2_da_to_db(mp, (xfs_dablk_t)bno);
+
 	/*
 	 * Update file's size if this is the data space and it grew.
 	 */
-- 
1.5.6