[XFS] Account for inode cluster alignment in all allocations

At ENOSPC, we can get a filesystem shutdown due to a cancelling a dirty
transaction in xfs_mkdir or xfs_create. This is due to the initial
allocation attempt not taking into account inode alignment and hence we
can prepare the AGF freelist for allocation when it's not actually
possible to do an allocation. This results in inode allocation returning
ENOSPC with a dirty transaction, and hence we shut down the filesystem.

Because the first allocation is an exact allocation attempt, we must tell
the allocator that the alignment does not affect the allocation attempt.
i.e. we will accept any extent alignment as long as the extent starts at
the block we want. Unfortunately, this means that if the longest free
extent is less than the length + alignment necessary for fallback
allocation attempts but is long enough to attempt a non-aligned
allocation, we will modify the free list.

If we then have the exact allocation fail, all other allocation attempts
will also fail due to the alignment constraint being taken into account.
Hence the initial attempt needs to set the "alignment slop" field so that
alignment, while not required, must be taken into account when determining
if there is enough space left in the AG to do the allocation.

That means if the exact allocation fails, we will not dirty the freelist
if there is not enough space available fo a subsequent allocation to
succeed. Hence we get an ENOSPC error back to userspace without shutting
down the filesystem.

SGI-PV: 978886
SGI-Modid: xfs-linux-melb:xfs-kern:30699a
Signed-off-by: NDavid Chinner <dgc@sgi.com>
Signed-off-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NLachlan McIlroy <lachlan@sgi.com>

fs/xfs/xfs_ialloc.c

@@ -107,6 +107,16 @@ xfs_ialloc_log_di(
 /*
  * Allocation group level functions.
  */
+static inline int
+xfs_ialloc_cluster_alignment(
+	xfs_alloc_arg_t	*args)
+{
+	if (xfs_sb_version_hasalign(&args->mp->m_sb) &&
+	    args->mp->m_sb.sb_inoalignmt >=
+	     XFS_B_TO_FSBT(args->mp, XFS_INODE_CLUSTER_SIZE(args->mp)))
+		return args->mp->m_sb.sb_inoalignmt;
+	return 1;
+}
 
 /*
  * Allocate new inodes in the allocation group specified by agbp.
@@ -167,10 +177,24 @@ xfs_ialloc_ag_alloc(
 		args.mod = args.total = args.wasdel = args.isfl =
 			args.userdata = args.minalignslop = 0;
 		args.prod = 1;
-		args.alignment = 1;
+
 		/*
-		 * Allow space for the inode btree to split.
+		 * We need to take into account alignment here to ensure that
+		 * we don't modify the free list if we fail to have an exact
+		 * block. If we don't have an exact match, and every oher
+		 * attempt allocation attempt fails, we'll end up cancelling
+		 * a dirty transaction and shutting down.
+		 *
+		 * For an exact allocation, alignment must be 1,
+		 * however we need to take cluster alignment into account when
+		 * fixing up the freelist. Use the minalignslop field to
+		 * indicate that extra blocks might be required for alignment,
+		 * but not to use them in the actual exact allocation.
 		 */
+		args.alignment = 1;
+		args.minalignslop = xfs_ialloc_cluster_alignment(&args) - 1;
+
+		/* Allow space for the inode btree to split. */
 		args.minleft = XFS_IN_MAXLEVELS(args.mp) - 1;
 		if ((error = xfs_alloc_vextent(&args)))
 			return error;
@@ -191,13 +215,8 @@ xfs_ialloc_ag_alloc(
 			ASSERT(!(args.mp->m_flags & XFS_MOUNT_NOALIGN));
 			args.alignment = args.mp->m_dalign;
 			isaligned = 1;
-		} else if (xfs_sb_version_hasalign(&args.mp->m_sb) &&
-			   args.mp->m_sb.sb_inoalignmt >=
-			   XFS_B_TO_FSBT(args.mp,
-			  	XFS_INODE_CLUSTER_SIZE(args.mp)))
-				args.alignment = args.mp->m_sb.sb_inoalignmt;
-		else
-			args.alignment = 1;
+		} else
+			args.alignment = xfs_ialloc_cluster_alignment(&args);
 		/*
 		 * Need to figure out where to allocate the inode blocks.
 		 * Ideally they should be spaced out through the a.g.
@@ -230,12 +249,7 @@ xfs_ialloc_ag_alloc(
 		args.agbno = be32_to_cpu(agi->agi_root);
 		args.fsbno = XFS_AGB_TO_FSB(args.mp,
 				be32_to_cpu(agi->agi_seqno), args.agbno);
-		if (xfs_sb_version_hasalign(&args.mp->m_sb) &&
-			args.mp->m_sb.sb_inoalignmt >=
-			XFS_B_TO_FSBT(args.mp, XFS_INODE_CLUSTER_SIZE(args.mp)))
-				args.alignment = args.mp->m_sb.sb_inoalignmt;
-		else
-			args.alignment = 1;
+		args.alignment = xfs_ialloc_cluster_alignment(&args);
 		if ((error = xfs_alloc_vextent(&args)))
 			return error;
 	}