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From: Bronek Kozicki <brok@incorrekt.com>
To: Tejun Heo <tj@kernel.org>, vcaputo@pengaru.com
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Date: Wed, 20 Dec 2017 18:04:12 +0000
Subject: Re: PROBLEM: NULL pointer dereference in kernel 4.14.6
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 <20171220151435.GB3413940@devbig577.frc2.facebook.com>
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On Wed, 20 Dec 2017, at 3:14 PM, Tejun Heo wrote:
> On Tue, Dec 19, 2017 at 05:42:39AM -0800, Tejun Heo wrote:
> > On Sun, Dec 17, 2017 at 03:24:48PM -0800, vcaputo@pengaru.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
> 

Thank you Tejun - I tested this fix and it works for me


B.