linux-ext4 - [PATCH 20/26] ext4: Protect extent conversion after DIO with i_dio

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Message-Id: <1369993379-13017-21-git-send-email-jack@suse.cz>
Date:	Fri, 31 May 2013 11:42:53 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ted Tso <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH 20/26] ext4: Protect extent conversion after DIO with i_dio_count

Make sure extent conversion after DIO happens while i_dio_count is still
elevated so that inode_dio_wait() waits until extent conversion is done.
This removes the need for explicit waiting for extent conversion in some
cases.

Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/inode.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1f9a8f9..4273b4d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3028,11 +3028,18 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 
 	BUG_ON(iocb->private == NULL);
 
+	/*
+	 * Make all waiters for direct IO properly wait also for extent
+	 * conversion. This also disallows race between truncate() and
+	 * overwrite DIO as i_dio_count needs to be incremented under i_mutex.
+	 */
+	if (rw == WRITE)
+		atomic_inc(&inode->i_dio_count);
+
 	/* If we do a overwrite dio, i_mutex locking can be released */
 	overwrite = *((int *)iocb->private);
 
 	if (overwrite) {
-		atomic_inc(&inode->i_dio_count);
 		down_read(&EXT4_I(inode)->i_data_sem);
 		mutex_unlock(&inode->i_mutex);
 	}
@@ -3135,9 +3142,10 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 	}
 
 retake_lock:
+	if (rw == WRITE)
+		inode_dio_done(inode);
 	/* take i_mutex locking again if we do a ovewrite dio */
 	if (overwrite) {
-		inode_dio_done(inode);
 		up_read(&EXT4_I(inode)->i_data_sem);
 		mutex_lock(&inode->i_mutex);
 	}
-- 
1.8.1.4

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