linux-kernel - Re: [PATCH v7 06/22] Replace XIP read and write with DAX I/O

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Date:	Wed, 9 Apr 2014 14:04:37 +0200
From:	Jan Kara <jack@...e.cz>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, willy@...ux.intel.com
Subject: Re: [PATCH v7 06/22] Replace XIP read and write with DAX I/O

  I've noticed one more thing here:

On Sun 23-03-14 15:08:32, Matthew Wilcox wrote:
....
> +ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode,
> +		const struct iovec *iov, loff_t offset, unsigned nr_segs,
> +		get_block_t get_block, dio_iodone_t end_io, int flags)
> +{
...
> +	retval = dax_io(rw, inode, iov, offset, end, get_block, &bh);
> +
> +	if ((flags & DIO_LOCKING) && (rw == READ))
> +		mutex_unlock(&inode->i_mutex);
> +
> +	inode_dio_done(inode);
> +
> +	if ((retval > 0) && end_io)
> +		end_io(iocb, offset, retval, bh.b_private);
  In direct IO code, we first call end_io() callback and do
inode_dio_done() only after that. Since filesystems use i_dio_count for
protecting against different races, calling end_io() after inode_dio_done()
can open all sorts of subtle races.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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