Re: PROBLEM: NULL pointer dereference in kernel 4.14.6

From: Bronek Kozicki
Date: Mon Dec 18 2017 - 14:56:26 EST

On 17/12/2017 23:24, vcaputo@xxxxxxxxxxx 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:

thank you, it certainly seems related. Is there some debugging option I could enable, or patch I could apply, which would make the point of data corruption easier to find? I'm ok taking untested patches, if that helps finding the location of the bug.