linux-kernel - Re: [PATCH v5 10/11] xfs: prepare xfs_break

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Date:   Sat, 10 Mar 2018 10:51:44 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, jack@...e.cz,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 10/11] xfs: prepare xfs_break_layouts() for another
        layout type

>  
> +int
> +xfs_break_layouts(
> +	struct inode		*inode,
> +	uint			*iolock,
> +	unsigned long		flags)
> +{
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	uint			iolock_assert = 0;
> +	int			ret = 0;
> +
> +	if (flags & XFS_BREAK_REMOTE)
> +		iolock_assert |= XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL;
> +	if (flags & XFS_BREAK_MAPS)
> +		iolock_assert |= XFS_MMAPLOCK_EXCL;
> +
> +	ASSERT(xfs_isilocked(ip, iolock_assert));
> +
> +	if (flags & XFS_BREAK_REMOTE)
> +		ret = xfs_break_leased_layouts(inode, iolock);
> +	return ret;

This just looks weird as hell.  We already pass in what to drop/reacquire
in the iolock argument.  I don't think we need another argument controlled
by the same callers to assert it.

> @@ -768,7 +790,7 @@ xfs_file_fallocate(
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	long			error;
>  	enum xfs_prealloc_flags	flags = 0;
> -	uint			iolock = XFS_IOLOCK_EXCL;
> +	uint			iolock = XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL;

This is a behavior change that should not be in a patch titled
"prepare xfs_break_layouts() for another layout type" but in one
explicitly changing this and documenting why.

In summary:  I think this should be replaced with a patch that
allows xfs_break_layouts to be called with the mmap lock held, and
change the callers that want the mmap lock to pass it with a good
explanation, and we should get rid of the XFS_BREAK_* flags here.
(need to check the next patch if there is any other good reason for
them to be added later, though).