linux-ext4 - [PATCH v2 4/6] ext4: reorder map.m_flags checks in ext4_iomap

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Date:   Mon, 9 Sep 2019 09:19:44 +1000
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        david@...morbit.com, hch@...radead.org, darrick.wong@...cle.com
Subject: [PATCH v2 4/6] ext4: reorder map.m_flags checks in ext4_iomap_begin()

For iomap direct IO write code path changes, we need to accommodate
for the case where the block mapping flags passed to ext4_map_blocks()
will result in m_flags having both EXT4_MAP_MAPPED and
EXT4_MAP_UNWRITTEN bits set. In order for the allocated unwritten
extents to be converted properly in the end_io handler, iomap->type
must be set to IOMAP_UNWRITTEN, so we need to reshuffle the
conditional statement in order to achieve this.

This change is a no-op for DAX code path as the block mapping flag
passed to ext4_map_blocks() when IS_DAX(inode) never results in
EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN being set at once.

Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
---
 fs/ext4/inode.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 761ce6286b05..efb184928e51 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3581,10 +3581,21 @@ 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 to ext4_map_blocks() for direct IO
+		 * writes can result in m_flags having both
+		 * EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits set. In
+		 * order for allocated unwritten extents to be
+		 * converted to written extents in the end_io handler
+		 * correctly, we need to ensure that the iomap->type
+		 * is also set appropriately in that case. Thus, 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;
-- 
2.20.1