On 7/10/22 17:11, Anup Patel wrote:
The kvm_riscv_check_vcpu_requests() is called with SRCU read lock held
and for KVM_REQ_SLEEP request it will block the VCPU without releasing
SRCU read lock. This causes KVM ioctls (such as KVM_IOEVENTFD) from
other VCPUs of the same Guest/VM to hang/deadlock if there is any
synchronize_srcu() or synchronize_srcu_expedited() in the path.
To fix the above in kvm_riscv_check_vcpu_requests(), we should do SRCU
read unlock before blocking the VCPU and do SRCU read lock after VCPU
wakeup.
Fixes: cce69aff689e ("RISC-V: KVM: Implement VCPU interrupts and
requests handling")
Reported-by: Bin Meng <bmeng.cn@xxxxxxxxx>
Thanks Anup for resolving the problem originally reported in
https://lore.kernel.org/all/5df27902-9009-afb9-68d3-186fdb4e4067@xxxxxxxxxxxxx/
Thanks to Bin for his analysis.
Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
With this patch applied to Linux v5.19-rc5 I am able to run U-Boot
qemu-riscv64_smode_defconfig on QEMU 7.0 with
qemu-system-riscv64 \
-M virt -accel kvm -m 2G -smp 2 \
-nographic \
-kernel u-boot \
-drive file=kinetic-server-cloudimg-riscv64.raw,format=raw,if=virtio \
-device virtio-net-device,netdev=eth0 \
-netdev user,id=eth0,hostfwd=tcp::8022-:22
and load files from the virtio drive.
Without the patch virtio access blocks:
[ +0.102462] INFO: task qemu-system-ris:1254 blocked for more than 120
seconds.
[ +0.004034] Not tainted 5.19.0-rc5 #4
[ +0.001145] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[ +0.002189] task:qemu-system-ris state:D stack: 0 pid: 1254 ppid:
1068 flags:0x00000000
[ +0.001546] Call Trace:
[ +0.000389] [<ffffffff806b1340>] schedule+0x42/0xaa
[ +0.008026] [<ffffffff806b6164>] schedule_timeout+0xa0/0xd4
[ +0.000086] [<ffffffff806b1c0a>] __wait_for_common+0x9a/0x19a
[ +0.000057] [<ffffffff806b1d24>] wait_for_completion+0x1a/0x22
[ +0.000053] [<ffffffff80063a88>] __synchronize_srcu.part.0+0x78/0xce
[ +0.000049] [<ffffffff80063b00>] synchronize_srcu_expedited+0x22/0x2c
[ +0.000474] [<ffffffff01417560>] kvm_swap_active_memslots+0x12e/0x170
[kvm]
[ +0.000864] [<ffffffff01419ad2>] kvm_set_memslot+0x1e8/0x388 [kvm]
[ +0.000267] [<ffffffff01419da6>] __kvm_set_memory_region+0x134/0x2f8 [kvm]
[ +0.000439] [<ffffffff0141d412>] kvm_vm_ioctl+0x1fc/0xba0 [kvm]
[ +0.000232] [<ffffffff80176af0>] sys_ioctl+0x80/0x96
[ +0.000129] [<ffffffff800032d2>] ret_from_syscall+0x0/0x2
Tested-by: Heinrich Schuchardt <heinrich.schuchardt@xxxxxxxxxxxxx>
---
arch/riscv/kvm/vcpu.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index b7a433c54d0f..5d271b597613 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -845,9 +845,11 @@ static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
if (kvm_request_pending(vcpu)) {
if (kvm_check_request(KVM_REQ_SLEEP, vcpu)) {
+ kvm_vcpu_srcu_read_unlock(vcpu);
rcuwait_wait_event(wait,
(!vcpu->arch.power_off) && (!vcpu->arch.pause),
TASK_INTERRUPTIBLE);
+ kvm_vcpu_srcu_read_lock(vcpu);
if (vcpu->arch.power_off || vcpu->arch.pause) {
/*
