|author||Christoph Hellwig <email@example.com>||2011-06-24 14:29:46 -0400|
|committer||Al Viro <firstname.lastname@example.org>||2011-07-20 20:47:48 -0400|
fs: always maintain i_dio_count
Maintain i_dio_count for all filesystems, not just those using DIO_LOCKING. This these filesystems to also protect truncate against direct I/O requests by using common code. Right now the only non-DIO_LOCKING filesystem that appears to do so is XFS, which uses an opencoded variant of the i_dio_count scheme. Behaviour doesn't change for filesystems never calling inode_dio_wait. For ext4 behaviour changes when using the dioread_nonlock option, which previously was missing any protection between truncate and direct I/O reads. For ocfs2 that handcrafted i_dio_count manipulations are replaced with the common code now enable. Signed-off-by: Christoph Hellwig <email@example.com> Signed-off-by: Al Viro <firstname.lastname@example.org>
Diffstat (limited to 'fs/direct-io.c')
1 files changed, 13 insertions, 12 deletions
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 354cbdbc14b..0a073c7125a 100644
@@ -297,8 +297,7 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is
aio_complete(dio->iocb, ret, 0);
- if (dio->flags & DIO_LOCKING)
@@ -1185,14 +1184,16 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
* For writes this function is called under i_mutex and returns with
* i_mutex held, for reads, i_mutex is not held on entry, but it is
* taken and dropped again before returning.
- * The i_dio_count counter keeps track of the number of outstanding
- * direct I/O requests, and truncate waits for it to reach zero.
- * New references to i_dio_count must only be grabbed with i_mutex
- * held.
* - if the flags value does NOT contain DIO_LOCKING we don't use any
* internal locking but rather rely on the filesystem to synchronize
* direct I/O reads/writes versus each other and truncate.
+ * To help with locking against truncate we incremented the i_dio_count
+ * counter before starting direct I/O, and decrement it once we are done.
+ * Truncate can wait for it to reach zero to provide exclusion. It is
+ * expected that filesystem provide exclusion between new direct I/O
+ * and truncates. For DIO_LOCKING filesystems this is done by i_mutex,
+ * but other filesystems need to take care of this on their own.
__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
@@ -1270,14 +1271,14 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
- * Will be decremented at I/O completion time.
+ * Will be decremented at I/O completion time.
* For file extending writes updating i_size before data
* writeouts complete can expose uninitialized blocks. So
* even for AIO, we need to wait for i/o to complete before