[PATCH 1/2] block: Ensure start sector is aligned for stacking atomic writes

[John Garry <john.g.garry@xxxxxxxxxx>]

For stacking atomic writes, ensure that the start sector is aligned with
the device atomic write unit min and any boundary. Otherwise, we may
permit misaligned atomic writes.

Rework bdev_can_atomic_write() into a common helper to resuse the
alignment check. There also use atomic_write_hw_unit_min, which is more
proper (than atomic_write_unit_min).

Fixes: d7f36dc446e89 ("block: Support atomic writes limits for stacked devices")
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 block/blk-settings.c   |  7 +++++--
 include/linux/blkdev.h | 21 ++++++++++++---------
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 8f09e33f41f6..a8dd5c097b8a 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -584,7 +584,7 @@ static bool blk_stack_atomic_writes_head(struct queue_limits *t,
 }
 
 static void blk_stack_atomic_writes_limits(struct queue_limits *t,
-				struct queue_limits *b)
+				struct queue_limits *b, sector_t start)
 {
 	if (!(t->features & BLK_FEAT_ATOMIC_WRITES_STACKED))
 		goto unsupported;
@@ -592,6 +592,9 @@ static void blk_stack_atomic_writes_limits(struct queue_limits *t,
 	if (!b->atomic_write_unit_min)
 		goto unsupported;
 
+	if (!blk_atomic_write_start_sect_aligned(start, b))
+		goto unsupported;
+
 	/*
 	 * If atomic_write_hw_max is set, we have already stacked 1x bottom
 	 * device, so check for compliance.
@@ -774,7 +777,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 		t->zone_write_granularity = 0;
 		t->max_zone_append_sectors = 0;
 	}
-	blk_stack_atomic_writes_limits(t, b);
+	blk_stack_atomic_writes_limits(t, b, start);
 
 	return ret;
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 378d3a1a22fc..b9776d469781 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1699,6 +1699,15 @@ struct io_comp_batch {
 	void (*complete)(struct io_comp_batch *);
 };
 
+static inline bool blk_atomic_write_start_sect_aligned(sector_t sector,
+						struct queue_limits *limits)
+{
+	unsigned int alignment = max(limits->atomic_write_hw_unit_min,
+				limits->atomic_write_hw_boundary);
+
+	return IS_ALIGNED(sector, alignment >> SECTOR_SHIFT);
+}
+
 static inline bool bdev_can_atomic_write(struct block_device *bdev)
 {
 	struct request_queue *bd_queue = bdev->bd_queue;
@@ -1707,15 +1716,9 @@ static inline bool bdev_can_atomic_write(struct block_device *bdev)
 	if (!limits->atomic_write_unit_min)
 		return false;
 
-	if (bdev_is_partition(bdev)) {
-		sector_t bd_start_sect = bdev->bd_start_sect;
-		unsigned int alignment =
-			max(limits->atomic_write_unit_min,
-			    limits->atomic_write_hw_boundary);
-
-		if (!IS_ALIGNED(bd_start_sect, alignment >> SECTOR_SHIFT))
-			return false;
-	}
+	if (bdev_is_partition(bdev))
+		return blk_atomic_write_start_sect_aligned(bdev->bd_start_sect,
+							limits);
 
 	return true;
 }
-- 
2.31.1