blk_validate_atomic_write_limits() ensures that any boundary fits into
and is aligned to any chunk size.

However, it should also be possible to fit the chunk size into any
boundary. That check is already made in
blk_stack_atomic_writes_boundary_head().

Relax the check in blk_validate_atomic_write_limits() by reusing (and
renaming) blk_stack_atomic_writes_boundary_head().

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 block/blk-settings.c | 66 +++++++++++++++++---------------------------
 1 file changed, 26 insertions(+), 40 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 8fa52914e16b0..54cffaae4df49 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -224,6 +224,27 @@ static void blk_atomic_writes_update_limits(struct queue_limits *lim)
 		lim->atomic_write_hw_boundary >> SECTOR_SHIFT;
 }
 
+/*
+ * Test whether any boundary is aligned with any chunk size. Stacked
+ * devices store any stripe size in t->chunk_sectors.
+ */
+static bool blk_valid_atomic_writes_boundary(unsigned int chunk_sectors,
+					unsigned int boundary_sectors)
+{
+	if (!chunk_sectors || !boundary_sectors)
+		return true;
+
+	if (boundary_sectors > chunk_sectors &&
+	    boundary_sectors % chunk_sectors)
+		return false;
+
+	if (chunk_sectors > boundary_sectors &&
+	    chunk_sectors % boundary_sectors)
+		return false;
+
+	return true;
+}
+
 static void blk_validate_atomic_write_limits(struct queue_limits *lim)
 {
 	unsigned int boundary_sectors;
@@ -264,20 +285,9 @@ static void blk_validate_atomic_write_limits(struct queue_limits *lim)
 		if (WARN_ON_ONCE(lim->atomic_write_hw_max >
 				 lim->atomic_write_hw_boundary))
 			goto unsupported;
-		/*
-		 * A feature of boundary support is that it disallows bios to
-		 * be merged which would result in a merged request which
-		 * crosses either a chunk sector or atomic write HW boundary,
-		 * even though chunk sectors may be just set for performance.
-		 * For simplicity, disallow atomic writes for a chunk sector
-		 * which is non-zero and smaller than atomic write HW boundary.
-		 * Furthermore, chunk sectors must be a multiple of atomic
-		 * write HW boundary. Otherwise boundary support becomes
-		 * complicated.
-		 * Devices which do not conform to these rules can be dealt
-		 * with if and when they show up.
-		 */
-		if (WARN_ON_ONCE(lim->chunk_sectors % boundary_sectors))
+
+		if (WARN_ON_ONCE(!blk_valid_atomic_writes_boundary(
+			lim->chunk_sectors, boundary_sectors)))
 			goto unsupported;
 
 		/*
@@ -644,31 +654,6 @@ static bool blk_stack_atomic_writes_tail(struct queue_limits *t,
 	return true;
 }
 
-/* Check for valid boundary of first bottom device */
-static bool blk_stack_atomic_writes_boundary_head(struct queue_limits *t,
-				struct queue_limits *b)
-{
-	unsigned int boundary_sectors;
-
-	if (!b->atomic_write_hw_boundary || !t->chunk_sectors)
-		return true;
-
-	boundary_sectors = b->atomic_write_hw_boundary >> SECTOR_SHIFT;
-
-	/*
-	 * Ensure atomic write boundary is aligned with chunk sectors. Stacked
-	 * devices store any stripe size in t->chunk_sectors.
-	 */
-	if (boundary_sectors > t->chunk_sectors &&
-	    boundary_sectors % t->chunk_sectors)
-		return false;
-	if (t->chunk_sectors > boundary_sectors &&
-	    t->chunk_sectors % boundary_sectors)
-		return false;
-
-	return true;
-}
-
 static void blk_stack_atomic_writes_chunk_sectors(struct queue_limits *t)
 {
 	unsigned int chunk_bytes;
@@ -706,7 +691,8 @@ static void blk_stack_atomic_writes_chunk_sectors(struct queue_limits *t)
 static bool blk_stack_atomic_writes_head(struct queue_limits *t,
 				struct queue_limits *b)
 {
-	if (!blk_stack_atomic_writes_boundary_head(t, b))
+	if (!blk_valid_atomic_writes_boundary(t->chunk_sectors,
+			b->atomic_write_hw_boundary >> SECTOR_SHIFT))
 		return false;
 
 	t->atomic_write_hw_unit_max = b->atomic_write_hw_unit_max;
-- 
2.43.5