[v6,01/11] ext4: reorder map.m_flags checks within ext4_iomap_begin()

Commit Message

Matthew Bobrowski Oct. 28, 2019, 10:50 a.m. UTC

For the direct I/O changes that follow in this patch series, we need
to accommodate for the case where the block mapping flags passed
through to ext4_map_blocks() result in m_flags having both
EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits set. In order for any
allocated unwritten extents to be converted correctly in the
->end_io() handler, the iomap->type must be set to IOMAP_UNWRITTEN for
cases where the EXT4_MAP_UNWRITTEN bit has been set within
m_flags. Hence the reason why we need to reshuffle this conditional
statement around.

This change is a no-op for DAX as the block mapping flags passed
through to ext4_map_blocks() i.e. EXT4_GET_BLOCKS_CREATE_ZERO never
results in both EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN being set at
once.

Signed-off-by: Matthew Bobrowski <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Reviewed-by: Ritesh Harjani <[e-mail]>
---
 fs/ext4/inode.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

Patch

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index abaaf7d96ca4..ee116344c420 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3535,10 +3535,20 @@  static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		iomap->type = delalloc ? IOMAP_DELALLOC : IOMAP_HOLE;
 		iomap->addr = IOMAP_NULL_ADDR;
 	} else {
-		if (map.m_flags & EXT4_MAP_MAPPED) {
-			iomap->type = IOMAP_MAPPED;
-		} else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
+		/*
+		 * Flags passed into ext4_map_blocks() for direct I/O writes
+		 * can result in m_flags having both EXT4_MAP_MAPPED and
+		 * EXT4_MAP_UNWRITTEN bits set. In order for any allocated
+		 * unwritten extents to be converted into written extents
+		 * correctly within the ->end_io() handler, we need to ensure
+		 * that the iomap->type is set appropriately. Hence the reason
+		 * why we need to check whether EXT4_MAP_UNWRITTEN is set
+		 * first.
+		 */
+		if (map.m_flags & EXT4_MAP_UNWRITTEN) {
 			iomap->type = IOMAP_UNWRITTEN;
+		} else if (map.m_flags & EXT4_MAP_MAPPED) {
+			iomap->type = IOMAP_MAPPED;
 		} else {
 			WARN_ON_ONCE(1);
 			return -EIO;