linux-kernel - Re: PROBLEM: NULL pointer dereference in kernel 4.14.6

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Message-ID: <20171220151435.GB3413940@devbig577.frc2.facebook.com>
Date:   Wed, 20 Dec 2017 07:14:35 -0800
From:   Tejun Heo <tj@...nel.org>
To:     vcaputo@...garu.com
Cc:     Bronek Kozicki <brok@...orrekt.com>, linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: NULL pointer dereference in kernel 4.14.6

On Tue, Dec 19, 2017 at 05:42:39AM -0800, Tejun Heo wrote:
> On Sun, Dec 17, 2017 at 03:24:48PM -0800, vcaputo@...garu.com wrote:
> > On Sun, Dec 17, 2017 at 05:49:44PM +0000, Bronek Kozicki wrote:
> > > I just upgraded to 4.14.7 and tried to reproduce this error, this time under strace. As you can see this happens when systemctl tries to read a specific entry under /sys/fs . In case this matters, the entry is for a small virtual machine running under qemu/kvm and managed by libvirt.
> > > 
> > > open("/sys/fs/cgroup/unified/machine.slice", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 5
> > > fstat(5, {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
> > > getdents(5, /* 12 entries */, 32768)    = 464
> > > openat(AT_FDCWD, "/sys/fs/cgroup/unified/machine.slice/machine-qemu\\x2d1\\x2dkartuzy\\x2dspice.scope/cgroup.procs", O_RDONLY|O_CLOEXEC) = 8
> > > fstat(8, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
> > > read(8,  <unfinished ...>)              = ?
> > > +++ killed by SIGKILL +++
> > > [1]    12078 killed     strace -- systemctl status
> > > 
> > > 
> > 
> > This recently came through lkml, may be related:
> > https://marc.info/?l=linux-kernel&m=151320108922415&w=2
> 
> It looks like it could be the same problem.  Working on the fix now.
> Will let you know when I have something.

Fix posted.

 http://lkml.kernel.org/r/20171220151331.GA3413940@devbig577.frc2.facebook.com

Thanks.

-- 
tejun