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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <55AF9EA8.6020102@redhat.com>
Date:	Wed, 22 Jul 2015 15:46:16 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Trond Myklebust <trond.myklebust@...marydata.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>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [RFC PATCH] nfs: avoid swap-over-NFS deadlock

On 07/22/2015 02:23 PM, Trond Myklebust wrote:
> 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?

I meant to cc Mel. Just added him.

AFAIK NFS is the only filesystem that uses swap_activate. Other
swapfiles are handled more or less like block device (divided in a set
of contiguous ranges of disk block called swap extents), so there are
not affected by this possible deadlock.

Also nfs_direct_IO() is special in that it is called only from swap,
nfs_file_direct_write() however has other users.

Jerome
> 
> Cheers
>   Trond
> 



Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)