Messages in this thread | | | Date | Tue, 1 Sep 2015 07:20:23 +0100 | From | "Richard W.M. Jones" <> | Subject | Re: [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler |
| |
On Sun, Aug 30, 2015 at 10:37:57PM -0400, Chuck Ebbert wrote: > This is from https://bugzilla.redhat.com/show_bug.cgi?id=1258223 > > [ 0.036000] BUG: unable to handle kernel paging request at 55501e06 [...] > [ 0.036000] [<c0409c80>] ? add_nops+0x90/0xa0 > [ 0.036000] [<c040a054>] apply_alternatives+0x274/0x630 > [ 0.036000] [<c07f1cf0>] ? wait_for_xmitr+0xa0/0xa0 > [ 0.036000] [<c071a6fc>] ? sprintf+0x1c/0x20 > [ 0.036000] [<c0aae480>] ? irq_entries_start+0x698/0x698 > [ 0.036000] [<c071be4b>] ? memcpy+0xb/0x30 > [ 0.036000] [<c07f3950>] ? serial8250_set_termios+0x20/0x20 [...] > Interrupt 0x30 occurred while the alternatives code was replacing the > initial 0x90,0x90,0x90 NOPs (from the ASM_CLAC macro) with the optimized > version, 0x8d,0x76,0x00. Only the first byte has been replaced so far, > and it makes a mess out of the insn decoding.
Chuck, thanks for reporting this.
I have only been able to reproduce this so far using qemu and TCG (not KVM) which of course raises a range of questions: could it be a qemu bug or a TCG bug? Could it be that an atomic op is not correctly implemented by qemu? I will keep trying on KVM. Because I don't have a convenient server with 32 bit kernel and a serial port that I can reboot thousands of times, I have not tried to reproduce on baremetal yet.
Here's how to reproduce it. (The host can be x86-64)
(1) Grab the 32 bit Fedora kernel we are using from https://kojipkgs.fedoraproject.org//packages/kernel/4.2.0/1.fc24/i686/kernel-core-4.2.0-1.fc24.i686.rpm (from http://koji.fedoraproject.org/koji/buildinfo?buildID=681723)
(2) Unpack it to extract vmlinuz:
cd /tmp rpm2cpio /mnt/scratch/kernel-core-4.2.0-1.fc24.i686.rpm | cpio -id cp ./lib/modules/4.2.0-1.fc24.i686/vmlinuz .
(3) Boot the kernel under qemu/KVM. The following single line command repeatedly boots the kernel until the bug is hit:
while qemu-system-x86_64 -nographic -no-reboot -M accel=kvm:tcg -kernel vmlinuz -append 'console=ttyS0 panic=1' -serial stdio -monitor none >& log; ! grep add_nops log; do echo -n .; done
It takes many iterations (100s with TCG) to hit the bug.
Rich.
-- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v
| |