Public bug reported:
[impact]
on shutdown of a guest, there is a race condition that results in qemu
crashing instead of normally shutting down. The bt looks similar to
this (depending on the specific version of qemu, of course; this is
taken from 2.5 version of qemu):
(gdb) bt
#0 __GI___pthread_mutex_lock (mutex=0x0) at ../nptl/pthread_mutex_lock.c:66
#1 0x00005636c0bc4389 in qemu_mutex_lock (mutex=mutex@entry=0x0) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/util/qemu-thread-posix.c:73
#2 0x00005636c0988130 in qemu_chr_fe_write_all (s=s@entry=0x0,
buf=buf@entry=0x7ffe65c086a0 "\v", len=len@entry=20) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/qemu-char.c:205
#3 0x00005636c08f3483 in vhost_user_write (msg=msg@entry=0x7ffe65c086a0,
fds=fds@entry=0x0, fd_num=fd_num@entry=0, dev=0x5636c1bf6b70,
dev=0x5636c1bf6b70)
at /build/qemu-7I4i1R/qemu-2.5+dfsg/hw/virtio/vhost-user.c:195
#4 0x00005636c08f411c in vhost_user_get_vring_base (dev=0x5636c1bf6b70,
ring=0x7ffe65c087e0) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/hw/virtio/vhost-user.c:364
#5 0x00005636c08efff0 in vhost_virtqueue_stop (dev=dev@entry=0x5636c1bf6b70,
vdev=vdev@entry=0x5636c2853338, vq=0x5636c1bf6d00, idx=1) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/hw/virtio/vhost.c:895
#6 0x00005636c08f2944 in vhost_dev_stop (hdev=hdev@entry=0x5636c1bf6b70,
vdev=vdev@entry=0x5636c2853338) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/hw/virtio/vhost.c:1262
#7 0x00005636c08db2a8 in vhost_net_stop_one (net=0x5636c1bf6b70,
dev=dev@entry=0x5636c2853338) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/hw/net/vhost_net.c:293
#8 0x00005636c08dbe5b in vhost_net_stop (dev=dev@entry=0x5636c2853338,
ncs=0x5636c209d110, total_queues=total_queues@entry=1) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/hw/net/vhost_net.c:371
#9 0x00005636c08d7745 in virtio_net_vhost_status (status=7 '\a',
n=0x5636c2853338) at /build/qemu-7I4i1R/qemu-2.5+dfsg/hw/net/virtio-net.c:150
#10 virtio_net_set_status (vdev=<optimized out>, status=<optimized out>) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/hw/net/virtio-net.c:162
#11 0x00005636c08ec42c in virtio_set_status (vdev=0x5636c2853338,
val=<optimized out>) at /build/qemu-7I4i1R/qemu-2.5+dfsg/hw/virtio/virtio.c:624
#12 0x00005636c098fed2 in vm_state_notify (running=running@entry=0,
state=state@entry=RUN_STATE_SHUTDOWN) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/vl.c:1605
#13 0x00005636c089172a in do_vm_stop (state=RUN_STATE_SHUTDOWN) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/cpus.c:724
#14 vm_stop (state=RUN_STATE_SHUTDOWN) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/cpus.c:1407
#15 0x00005636c085d240 in main_loop_should_exit () at
/build/qemu-7I4i1R/qemu-2.5+dfsg/vl.c:1883
#16 main_loop () at /build/qemu-7I4i1R/qemu-2.5+dfsg/vl.c:1931
#17 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at
/build/qemu-7I4i1R/qemu-2.5+dfsg/vl.c:4683
[test case]
unfortunately since this is a race condition, it's very hard to
arbitrarily reproduce; it depends very much on the overall configuration
of the guest as well as how exactly it's shut down - specifically, its
vhost user net must be closed from the host side at a specific time
during qemu shutdown.
I have someone with such a setup who has reported to me their setup is
able to reproduce this reliably, but the config is too complex for me to
reproduce so I have relied on their reproduction and testing to debug
and craft the patch for this.
[regression potential]
the change adds flags to prevent repeated calls to both vhost_net_stop()
and vhost_net_cleanup() (really, prevents repeated calls to
vhost_dev_cleanup()). Any regression would be seen when stopping and/or
cleaning up a vhost net. Regressions might include failure to hot-
remove a vhost net from a guest, or failure to cleanup (i.e. mem leak),
or crashes during cleanup or stopping a vhost net.
[other info]
this was originally seen in the 2.5 version of qemu - specifically, the
UCA version in trusty-mitaka (which uses the xenial qemu codebase).
However, this appears to still apply upstream, and I am sending a patch
to the qemu list to patch upstream as well.
** Affects: qemu (Ubuntu)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Affects: qemu (Ubuntu Xenial)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Affects: qemu (Ubuntu Bionic)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Affects: qemu (Ubuntu Cosmic)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Affects: qemu (Ubuntu Disco)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Also affects: qemu (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Disco)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Cosmic)
Importance: Undecided
Status: New
** Changed in: qemu (Ubuntu Disco)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: qemu (Ubuntu Cosmic)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: qemu (Ubuntu Bionic)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: qemu (Ubuntu Xenial)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: qemu (Ubuntu Disco)
Importance: Undecided => Medium
** Changed in: qemu (Ubuntu Cosmic)
Importance: Undecided => Medium
** Changed in: qemu (Ubuntu Bionic)
Importance: Undecided => Medium
** Changed in: qemu (Ubuntu Disco)
Status: New => In Progress
** Changed in: qemu (Ubuntu Cosmic)
Status: New => In Progress
** Changed in: qemu (Ubuntu Bionic)
Status: New => In Progress
** Changed in: qemu (Ubuntu Xenial)
Status: New => In Progress
** Changed in: qemu (Ubuntu Xenial)
Importance: Undecided => Medium
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https://bugs.launchpad.net/bugs/1823458
Title:
race condition between vhost_net_stop and CHR_EVENT_CLOSED on shutdown
crashes qemu
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