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 <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 354cbdb..0a073c7 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -297,8 +297,7 @@
aio_complete(dio->iocb, ret, 0);
}
- if (dio->flags & DIO_LOCKING)
- inode_dio_done(dio->inode);
+ inode_dio_done(dio->inode);
return ret;
}
@@ -1185,14 +1184,16 @@
* 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.
*/
ssize_t
__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
@@ -1270,14 +1271,14 @@
goto out;
}
}
-
- /*
- * Will be decremented at I/O completion time.
- */
- atomic_inc(&inode->i_dio_count);
}
/*
+ * Will be decremented at I/O completion time.
+ */
+ atomic_inc(&inode->i_dio_count);
+
+ /*
* 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