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fs: always maintain i_dio_count

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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>
This commit is contained in:
Christoph Hellwig
2011-06-24 14:29:46 -04:00
committed by Al Viro
parent 562c72aa57
commit df2d6f2658
3 changed files with 17 additions and 24 deletions
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25
fs/direct-io.c
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@@ -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)
inode_dio_done(dio->inode);
inode_dio_done(dio->inode);
return ret;
}
@@ -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.
*/
ssize_t
__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
@@ -1270,13 +1271,13 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
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