Hi Mel, all,

My kernel on qemu/arm64 setup hangs at early boot since v5.0-rc1.
Backtrace is not too verbose:
(gdb) i threads
  Id   Target Id         Frame
* 1    Thread 1 (CPU#0 [running]) 0xffff000010a49b74 in __delay (cycles=4096)
    at arch/arm64/lib/delay.c:49
  2    Thread 2 (CPU#1 [halted ]) 0x0000000000000000 in ?? ()
  3    Thread 3 (CPU#2 [halted ]) 0x0000000000000000 in ?? ()
  4    Thread 4 (CPU#3 [halted ]) 0x0000000000000000 in ?? ()
(gdb) bt
#0  0xffff000010a49b74 in __delay (cycles=4096) at arch/arm64/lib/delay.c:49
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Reverting the patch
1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external
fragmentation event occurs") together with following patch
73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held")
helps me to boot normally. 

Some system information is below, and config is attached.

Thanks,
Yury

$ qemu-system-aarch64 --version
QEMU emulator version 2.11.1(Debian 1:2.11+dfsg-1ubuntu7.9)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

$ cat runlinux.sh
TAP=tap0
BRIDGE=br0
NETWORK="-device virtio-net-device,netdev=netdev0 -netdev tap,ifname=$TAP,script=no,id=netdev0"

sudo ip tuntap add mode tap dev $TAP
sudo ip link set dev $TAP promisc on
sudo ip link set dev $TAP up
sudo ip link set dev $TAP master $BRIDGE

qemu-system-aarch64 -machine virt -cpu cortex-a57 -nographic -smp 4 -m 1024 \
	-machine virt -cpu cortex-a57 -nographic -smp 4 -m 1024 \
	-machine virt -cpu cortex-a57 -nographic -smp 4  -m 1024 \
	-global virtio-blk-device.scsi=off -device virtio-scsi-device,id=scsi \
	-drive file=img/ubuntu-core-14.04.1-core-arm64.img,id=coreimg,cache=unsafe,if=none -device scsi-hd,drive=coreimg \
	-kernel /home/yury/work/linux/arch/arm64/boot/Image \
	--append "rcu_nocbs=2-3 irqaffinity=0 task_isolation_debug console=ttyAMA0 root=/dev/sda nohz_full=2-3 isolcpus=2-3 task_isolation=2-3" \
	-initrd initrd.img-3.13.0-62-generic \
	$NETWORK \
	-redir tcp:2222::22 \
	-s \
	$@

sudo ip link set dev $TAP nomaster
sudo ip link set dev $TAP down
sudo ip link set dev $TAP promisc off
sudo ip tuntap del mode tap dev $TAP