From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bronek Kozicki Subject: Re: PROBLEM: NULL pointer dereference in kernel 4.14.6 Date: Mon, 18 Dec 2017 19:56:17 +0000 Message-ID: <95d82ae1-fe4c-4eee-8e94-fa0df3e25532@incorrekt.com> References: <1513512885.3653140.1207725096.395A9CCC@webmail.messagingengine.com> <08995310-d853-ee77-ed1f-26cc336a4a30@incorrekt.com> <20171217232448.yfaxxew2ijaay7iu@shells.gnugeneration.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=incorrekt.com; h=cc:content-transfer-encoding:content-type:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; bh=gsm7tlbG4htZ9rHsN GfZzrJoLHJltM+Yq+ny2kJKjOA=; b=HLoqx8mQzC84wZvd5MOGGCsM3BZDfMOwg K//36gKmH4OIHOeARMAow2MSiH5fydUSKaIYmY1T/i2B/snOYNIgjE+COtbnOHvq oPHiGOZy+I0e2iCwry4tBl7yxeDndE/gadiXIiahYpof67MyUNztrEalgFrNxp7U 17FJuRPdg3sXJgk9zASKb+YgaLb+MZqmzHIO6cpcJUi+QzdoNmsD6EMafln0Ct+m wjEfg+6Cwf0f8Q8vq0FBAA72VPN9RDYk3a1yu/85KqJLt9XyrJHZgbLAy0293o8R 4vHIouYC/R2hjzQeY0scDA7gC/vb29G92HIhdOVs4rIOlzMvdU4Jw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-me-sender:x-me-sender:x-sasl-enc; s=fm1; bh=gsm7tl bG4htZ9rHsNGfZzrJoLHJltM+Yq+ny2kJKjOA=; b=joZGirbigvSH5XOUm2Ow5c LFhQL4IBus+olIbAsbHTCy8AN2roo1mxv+DQ9FL9UpErKKPIO/WxFXpzafyRYZQb XuqAbj2lxTH0x5Rx2vmarlXqjHTinEcpr5g0m8LhOTYPnB0D/nTWRra2bN4GBEec KkIjYji74kMN52OuTPFtQff2ThKbxRqJ+fBEYUsGrb7jyW829r14X6vQD1C/0+/p GOBtPFfZ+ezQ2KVsUgHq0L/irQ2d/4zUiRuk+w/TJ+BowIl/169aCBBCWYUj2zHd gXMaJNQfz+xTfn5K4FgeMGSqaapXS2j/6frUXg77KjD5qHSG1UarRHSmcwbnHR7w == In-Reply-To: <20171217232448.yfaxxew2ijaay7iu-5Y5FpTStZqUl8ZggnyUIT4tm+1EbUQKi@public.gmane.org> Content-Language: en-GB Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: vcaputo-IiWei5kqaphBDgjK7y7TUQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 17/12/2017 23:24, vcaputo-IiWei5kqaphBDgjK7y7TUQ@public.gmane.org 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, ) = ? >> +++ 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 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. B.