linux-kernel - Re: splice read/write pipe lock ordering issues (was Re: XFS lockdep with Linux v3.17-5503-g35a9ad8af0bb)

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Date:	Fri, 17 Oct 2014 02:38:36 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	linux-fsdevel@...r.kernel.org, Eric Sandeen <sandeen@...hat.com>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	viro@...IV.linux.org.uk, xfs@....sgi.com
Subject: Re: splice read/write pipe lock ordering issues (was Re: XFS lockdep
 with Linux v3.17-5503-g35a9ad8af0bb)

On Fri, Oct 17, 2014 at 09:14:34AM +1100, Dave Chinner wrote:
> That smells like a splice architecture bug. splice write puts the
> pipe lock outside the inode locks, but splice read puts the pipes
> locks *inside* the inode locks.
> 
> The recent commit 8d02076 "(->splice_write() via ->write_iter()")
> which went into 3.16 will be what is causing this. It replaced a
> long standing splice lock inversion problem (XFS iolock vs i_mutex
> http://oss.sgi.com/archives/xfs/2011-08/msg00122.html) by moving
> to a ->write_iter call under the pipe_lock.
> 
> Only XFS reports this issue because XFS is the only filesystem that
> serialises splice reads against truncate, concurrent writes into the
> same region, extent manipulation functions via fallocate() (e.g.
> hole punch), etc. and it does so via the inode iolock that it takes
> in shared (read) mode during xfs_file_splice_read().

Actually ocfs2 and nfs will have the same issue.

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