linux-kernel - Re: [RFC PATCH] nfs: avoid swap-over-NFS deadlock

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Message-ID: <CAHQdGtRXhUi+=akuASUWo-tYy0YCWJtUts6fqGnA62fo1Jf5tA@mail.gmail.com>
Date:	Wed, 22 Jul 2015 08:23:45 -0400
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	Anna Schumaker <anna.schumaker@...app.com>,
	Christoph Hellwig <hch@...radead.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] nfs: avoid swap-over-NFS deadlock

On Wed, Jul 22, 2015 at 4:10 AM, Jerome Marchand <jmarchan@...hat.com> wrote:
>
> Lockdep warns about a inconsistent {RECLAIM_FS-ON-W} ->
> {IN-RECLAIM_FS-W} usage. The culpritt is the inode->i_mutex taken in
> nfs_file_direct_write(). This code was introduced by commit a9ab5e840669
> ("nfs: page cache invalidation for dio").
> This naive test patch avoid to take the mutex on a swapfile and makes
> lockdep happy again. However I don't know much about NFS code and I
> assume it's probably not the proper solution. Any thought?
>
> Signed-off-by: Jerome Marchand <jmarchan@...hat.com>

NFS is not the only O_DIRECT implementation to set the inode->i_mutex.
Why can't this be fixed in the generic swap code instead of adding
yet-another-exception-for-IS_SWAPFILE?

Cheers
  Trond
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