Received-SPF: pass (google.com: best guess record for domain of linux-ext4-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 5 Nov 2019 22:59:37 +1100
From:   Matthew Bobrowski <mbobrowski@mbobrowski.org>
To:     tytso@mit.edu, jack@suse.cz, adilger.kernel@dilger.ca
Cc:     linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        riteshh@linux.ibm.com
Subject: [PATCH v7 03/11] ext4: iomap that extends beyond EOF should be
 marked dirty
Message-ID: <8b43ee9ee94bee5328da56ba0909b7d2229ef150.1572949325.git.mbobrowski@mbobrowski.org>
References: <cover.1572949325.git.mbobrowski@mbobrowski.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <cover.1572949325.git.mbobrowski@mbobrowski.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

This patch addresses what Dave Chinner had discovered and fixed within
commit: 7684e2c4384d. This changes does not have any user visible
impact for ext4 as none of the current users of ext4_iomap_begin()
that extend files depend on IOMAP_F_DIRTY.

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@mbobrowski.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
---
 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 f33fa86fff67..b422d9b8c0bd 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3565,8 +3565,14 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			return ret;
 	}
 
+	/*
+	 * 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;
 	iomap->bdev = inode->i_sb->s_bdev;
 	iomap->dax_dev = sbi->s_daxdev;
-- 
2.20.1