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Subject: Re: [nfsd4] potentially hardware breaking regression in 4.14-rc and
 4.13.11
To:     "J. Bruce Fields" <bfields@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        stable <stable@vger.kernel.org>,
        Thorsten Leemhuis <regressions@leemhuis.info>
References: <a17842c3-aae7-da98-424e-4441dd727e6d@gentoo.org>
 <CA+55aFzGDyeJctD5Y3paBnysWXbA0cMF1_7mvvzG3n2OAnNhHw@mail.gmail.com>
 <20171109204757.GB11619@parsley.fieldses.org>
From:   Patrick McLean <chutzpah@gentoo.org>
Message-ID: <a4037a45-225c-f4b9-5f5e-555f4fc3a36f@gentoo.org>
Date:   Thu, 9 Nov 2017 15:07:15 -0800
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On 2017-11-09 12:47 PM, J. Bruce Fields wrote:
> On Wed, Nov 08, 2017 at 06:40:22PM -0800, Linus Torvalds wrote:
>> Anyway, that cmovne noise makes it a bit hard to see the actual part
>> that matters (and that traps) but I'm almost certain that it's the
>> "mnt->mnt_sb->s_flags" loading that is part of calculate_f_flags()
>> when it then does
>>
>>      flags_by_sb(mnt->mnt_sb->s_flags);
>>
>> and I think mnt->mnt_sb is NULL. We know it's not 'mnt' itself that is
>> NULL, because we wouldn't have gotten this far if it was.
>>
>> Now, afaik, mnt->mnt_sb should never be NULL in the first place for a
>> proper path. And the vfs_statfs() code itself hasn't changed in a
>> while.
>>
>> Which does seem to implicate nfsd as having passed in a bad path to
>> vfs_statfs(). But I'm not seeing any changes in nfsd either.
>>
>> In particular, there are *no* nfsd changes in that 4.13.8..4.13.11
>> range. There is a bunch of xfs changes, though. What's the underlying
>> filesystem that you are exporting?
>>
>> But bringing in Al Viro and Bruce Fields explicitly in case they see
>> something. And Darrick, just in case it might be xfs.
> 
> Looking at https://lkml.org/lkml/2017/11/8/1086 for the actual oops...
> 
> It doesn't remind me of any known issue.
> 
> So either I'm overlooking something or the bug's elsewhere.
> 
> It sounds like you're varying *only* the server version, so there's not
> much chance that this could be triggered by changes in client behavior?
> 

We are definitely only varying the kernel on the server, nothing on the
client side is changing. The client in this case is essentially an
embedded device that we do not have a whole lot of control over.

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