[Qemu-devel] Qemu hanging

[Filipe Manana]

Hello,

Recently qemu started hanging when running fstests (xfstests) after
upgrading the guests kernel (linux) from 4.15.x to 4.16. Nothing else
changed in the host or guest, besides the kernel version in the guest.

Running fstests always hangs when running either the test generic/299
or generic/451. But it happens only when running all the generic tests
in sequence, running any of those two tests in isolation doesn't hang
qemu (so far at least).

I tried with qemu versions 2.11.2,  2.12.1 and 3.0.0. It hangs with
any of these versions. The issue happens with any linux kernel version
>= 4.16 (including latest 4.19-rc5) in the guest.
Initially I noticed this when testing btrfs with fstests but later
checked that it happens as well when testing xfs.

I captured a coredump (using qemu 3.0.0) and it's available at:

https://www.dropbox.com/s/c3ntm5galaz4r83/core_dump.tar.xz?dl=0

The stack traces of all the qemu threads are pasted here (not every helpful):

https://friendpaste.com/hmCX2IG3VrA233uNtw1MP

This happens on 2 different physical machines (x86_64, running
different linux distros with different kernel versions) even when
using new guests.

qemu is invoked with the following script/config:

https://friendpaste.com/hmCX2IG3VrA233uNuFRNc

Anything else I can provide to help debug this?

Thanks.