linux-ext4 - [PATCH v7 01/11] ext4: reorder map.m_flags checks within ext4_iomap

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Date:   Tue, 5 Nov 2019 22:58:55 +1100
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,
        riteshh@...ux.ibm.com
Subject: [PATCH v7 01/11] ext4: reorder map.m_flags checks within
 ext4_iomap_begin()

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 <mbobrowski@...browski.org>
Reviewed-by: Jan Kara <jack@...e.cz>
Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
---
 fs/ext4/inode.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0d8971b819e9..e4b0722717b3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3577,10 +3577,20 @@ 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;
-- 
2.20.1