linux-kernel - Re: [PATCH 1/1] fix d_revalidate oopsen on NFS exports

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Message-ID: <20111201053255.GA6831@onthe.net.au>
Date:	Thu, 1 Dec 2011 16:32:55 +1100
From:	Chris Dunlop <chris@...he.net.au>
To:	Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:	David Howells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Eric Van Hensbergen <ericvh@...il.com>,
	Ron Minnich <rminnich@...dia.gov>,
	Latchesar Ionkov <lucho@...kov.net>,
	Jan Harkes <jaharkes@...cmu.edu>,
	"maintainer@...he.net.au:CODA FILE SYSTEM" <coda@...cmu.edu>,
	Petr Vandrovec <petr@...drovec.name>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	v9fs-developer@...ts.sourceforge.net,
	linux-afs@...ts.infradead.org, codalist@...EMANN.coda.cs.cmu.edu,
	jfs-discussion@...ts.sourceforge.net, linux-nfs@...r.kernel.org
Subject: Re: [PATCH 1/1] fix d_revalidate oopsen on NFS exports

On Wed, Nov 30, 2011 at 09:53:16PM -0600, Dave Kleikamp wrote:
> On 11/30/2011 09:33 PM, Chris Dunlop wrote:
>> On Wed, Nov 30, 2011 at 08:22:39PM -0600, Dave Kleikamp wrote:
>>> On 11/30/2011 06:47 PM, Chris Dunlop wrote:
>>>>> It's also worth printing a message - this *is* a kernel bug of some description
>>>>> if it happens.
>>>>
>>>> Like the below?  This covers the d_revalidate for 9p, afs, coda,
>>>> hfs, ncpfs, proc, sysfs.
>>>>
>>>> Note:  jfs isn't susceptible to this problem, but the resolution
>>>> doesn't look like the other file systems, and from the comment
>>>> I'm not sure if the problem was really understood and if it's
>>>> doing the right thing:
>>>
>>> This code, as well as the comments, were copied from vfat. It seems
>>> reasonable for case-insensitive but case-preserving behavior (not jfs's
>>> default). The safe thing is to drop the negative dentry if we don't know
>>> the operation.
>> 
>> In that case, it looks like the thing to do might be to add the
>> "protection" to the start of jfs_ci_revaliate(), per how the
>> original has been changed in vfat:
> 
> The LOOKUP_RCU check had previously been there, but Al Viro removed it:
> 
> commit 5c0f360b083fb33d05d1bff4b138b82d715eb419
> Author: Al Viro <viro@...iv.linux.org.uk>
> Date:   Sat Jun 25 21:41:09 2011 -0400
> 
>     jfs_ci_revalidate() is safe from RCU mode
> 
> I'm not sure what it takes to be "safe", but this is a simple function
> that doesn't block, take locks, or do much of anything. You shouldn't
> need to do anything with jfs.
> 
> Shaggy

OK, thanks.

Chris
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