Re: Regression: sched/preempt: Add static_key() to preempt_notifiers breaks my KVM

Peter Zijlstra
2015-06-25T12:09:57Z

On Thu, Jun 25, 2015 at 02:00:02PM +0200, Pontus Fuchs wrote:
> Hi,
>
> On 4.1+ kernels I can no longer start my KVM guest. Upon trying to start it
> I can see the following log message:
>
> [ 25.821060] BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:97
> [ 25.821063] in_atomic(): 1, irqs_disabled(): 0, pid: 2113, name:
> qemu-system-x86
> [ 25.821066] CPU: 0 PID: 2113 Comm: qemu-system-x86 Not tainted 4.1.0+ #88
> [ 25.821067] Hardware name: Dell Inc. Dell System XPS 15Z/00WW5M,
> BIOS A12 09/07/2012
> [ 25.821068] 0000000000000061 ffff88021339bcd8 ffffffff816b8c81
> 0000000000000007
> [ 25.821070] ffff880231159d40 ffff88021339bcf8 ffffffff8107d163
> ffff88021339bd18
> [ 25.821072] ffffffff81a451bc ffff88021339bd28 ffffffff8107d1ed
> ffff8802133a0000
> [ 25.821073] Call Trace:
> [ 25.821078] [<ffffffff816b8c81>] dump_stack+0x4c/0x65
> [ 25.821081] [<ffffffff8107d163>] ___might_sleep+0xd3/0x110
> [ 25.821083] [<ffffffff8107d1ed>] __might_sleep+0x4d/0x90
> [ 25.821085] [<ffffffff816bde74>] mutex_lock+0x24/0x50
> [ 25.821087] [<ffffffff81141ef7>] static_key_slow_inc+0x57/0xc0
> [ 25.821089] [<ffffffff8107cafd>] preempt_notifier_register+0x1d/0x60
> [ 25.821099] [<ffffffffa04f11fd>] vcpu_load+0x3d/0x70 [kvm]
> [ 25.821108] [<ffffffffa050699e>] kvm_arch_vcpu_setup+0x1e/0x50 [kvm]
> [ 25.821115] [<ffffffffa05066e1>] ? kvm_arch_vcpu_create+0x51/0x70 [kvm]
> [ 25.821120] [<ffffffffa04f29b2>] kvm_vm_ioctl+0x1d2/0x7a0 [kvm]
> [ 25.821123] [<ffffffff811b7881>] do_vfs_ioctl+0x301/0x550
> [ 25.821124] [<ffffffff811b7b49>] SyS_ioctl+0x79/0x90
> [ 25.821127] [<ffffffff816c0257>] entry_SYSCALL_64_fastpath+0x12/0x6a
>

That seems pointless..

---
virt/kvm/kvm_main.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 90977418aeb6..d7aafa0458a0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -128,8 +128,9 @@ int vcpu_load(struct kvm_vcpu *vcpu)

if (mutex_lock_killable(&vcpu->mutex))
return -EINTR;
- cpu = get_cpu();
preempt_notifier_register(&vcpu->preempt_notifier);
+
+ cpu = get_cpu();
kvm_arch_vcpu_load(vcpu, cpu);
put_cpu();
return 0;
@@ -139,8 +140,8 @@ void vcpu_put(struct kvm_vcpu *vcpu)
{
preempt_disable();
kvm_arch_vcpu_put(vcpu);
- preempt_notifier_unregister(&vcpu->preempt_notifier);
preempt_enable();
+ preempt_notifier_unregister(&vcpu->preempt_notifier);
mutex_unlock(&vcpu->mutex);
}