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

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Message-ID: <20171219134239.GN3919388@devbig577.frc2.facebook.com>
Date:   Tue, 19 Dec 2017 05:42:39 -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 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.

Thanks.

-- 
tejun