When testing live migration with multifd channels (8, 16, or a bigger number)
and using qemu -incoming (without "defer"), if a network error occurs
(for example, triggering the kernel SYN flooding detection),
the migration fails and the guest hangs forever.
The test environment and the command line is as the following:
QEMU verions: QEMU emulator version 6.2.91 (v6.2.0-rc1-47-gc5fbdd60cf)
Host OS: SLE 15 with kernel: 5.14.5-1-default
Network Card: mlx5 100Gbps
Network card: Intel Corporation I350 Gigabit (1Gbps)
Source:
qemu-system-x86_64 -M q35 -smp 32 -nographic \
-serial telnet:10.156.208.153:4321,server,nowait \
-m 4096 -enable-kvm -hda /var/lib/libvirt/images/openSUSE-15.3.img \
-monitor stdio
Dest:
qemu-system-x86_64 -M q35 -smp 32 -nographic \
-serial telnet:10.156.208.154:4321,server,nowait \
-m 4096 -enable-kvm -hda /var/lib/libvirt/images/openSUSE-15.3.img \
-monitor stdio \
-incoming tcp:1.0.8.154:4000
(qemu) migrate_set_parameter max-bandwidth 100G
(qemu) migrate_set_capability multifd on
(qemu) migrate_set_parameter multifd-channels 16
The guest hangs when executing the command: migrate -d tcp:1.0.8.154:4000.
If a network problem happens, TCP ACK is not received by destination
and the destination resets the connection with RST.
No. Time Source Destination Protocol Length Info
119 1.021169 1.0.8.153 1.0.8.154 TCP 1410 60166 →
4000 [PSH, ACK] Seq=65 Ack=1 Win=62720 Len=1344 TSval=1338662881
TSecr=1399531897
No. Time Source Destination Protocol Length Info
125 1.021181 1.0.8.154 1.0.8.153 TCP 54 4000 →
60166 [RST] Seq=1 Win=0 Len=0
kernel log:
[334520.229445] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[334562.994919] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[334695.519927] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[334734.689511] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[335687.740415] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[335730.013598] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
There are two problems here:
1. On the send side, the main thread is blocked on qemu_thread_join and
send threads are blocked on sendmsg
2. On receive side, the receive threads are blocked on qemu_sem_wait to
wait for a semaphore.
The patch is to fix the first problem, and the guest doesn't hang any more.
But there is no better solution to fix the second problem yet.
Li Zhang (1):
multifd: Shut down the QIO channels to avoid blocking the send threads
when they are terminated.
migration/multifd.c | 3 +++
1 file changed, 3 insertions(+)
--
2.31.1
