linux-kernel - Re: dcache_readdir NULL inode oops

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Message-ID: <20181110111656.GA16667@hc>
Date:   Sat, 10 Nov 2018 11:17:03 +0000
From:   Jan Glauber <Jan.Glauber@...ium.com>
To:     Will Deacon <will.deacon@....com>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: dcache_readdir NULL inode oops

On Fri, Nov 09, 2018 at 03:58:56PM +0000, Will Deacon wrote:
> On Fri, Nov 09, 2018 at 02:37:51PM +0000, Jan Glauber wrote:
> > I'm seeing the following oops reproducible with upstream kernel on arm64
> > (ThunderX2):
> 
> [...]
> 
> > It happens after 1-3 hours of running 'stress-ng --dev 128'. This testcase
> > does a scandir of /dev and then calls random stuff like ioctl, lseek,
> > open/close etc. on the entries. I assume no files are deleted under /dev
> > during the testcase.
> >
> > The NULL pointer is the inode pointer of next. The next dentry->d_flags is
> > DCACHE_RCUACCESS when this happens.
> >
> > Any hints on how to further debug this?
> 
> Can you reproduce the issue with vanilla -rc1 and do you have a "known good"
> kernel?

I can try out -rc1, but IIRC this wasn't bisectible as the bug was present at
least back to 4.14. I need to double check that as there were other issues
that are resolved now so I may confuse things here. I've defintely seen
the same bug with 4.18.

Unfortunately I lost access to the machine as our data center seems to be
moving currently so it might take some days until I can try -rc1.

thanks,
Jan