linux-ext4 - [PATCH v5 02/12] ext4: iomap that extends beyond EOF should be marked dirty

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Message-ID: <995387be9841bde2151c85880555c18bec68a641.1571647179.git.mbobrowski@mbobrowski.org>
Date:   Mon, 21 Oct 2019 20:17:46 +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,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: [PATCH v5 02/12] ext4: iomap that extends beyond EOF should be
 marked dirty

This patch is effectively addressed what Dave Chinner had found and
fixed within this commit: 8a23414ee345. Justification for needing this
modification has been provided below:

When doing a direct IO that spans the current EOF, and there are
written blocks beyond EOF that extend beyond the current write, the
only metadata update that needs to be done is a file size extension.

However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
there is IO completion metadata updates required, and hence we may
fail to correctly sync file size extensions made in IO completion when
O_DSYNC writes are being used and the hardware supports FUA.

Hence when setting IOMAP_F_DIRTY, we need to also take into account
whether the iomap spans the current EOF. If it does, then we need to
mark it dirty so that IO completion will call generic_write_sync() to
flush the inode size update to stable storage correctly.

Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
---
 fs/ext4/inode.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 158eea9a1944..0dd29ae5cc8c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3412,8 +3412,14 @@ static void ext4_set_iomap(struct inode *inode, struct iomap *iomap,
 {
 	u8 blkbits = inode->i_blkbits;

+	/*
+	 * Writes that span EOF might trigger an I/O size update on completion,
+	 * so consider them to be dirty for the purposes of O_DSYNC, even if
+	 * there is no other metadata changes being made or are pending here.
+	 */
 	iomap->flags = 0;
-	if (ext4_inode_datasync_dirty(inode))
+	if (ext4_inode_datasync_dirty(inode) ||
+	    offset + length > i_size_read(inode))
 		iomap->flags |= IOMAP_F_DIRTY;

 	if (map->m_flags & EXT4_MAP_NEW)
-- 
2.20.1

--<M>--