commit 3898da947bba ("KVM: avoid using rcu_dereference_protected") can
trigger the following lockdep/rcu splat if the VM_CREATE ioctl fails,
for example if kvm_arch_init_vm fails:
WARNING: suspicious RCU usage
4.13.0+ #105 Not tainted
-----------------------------
./include/linux/kvm_host.h:481 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
no locks held by qemu-system-s39/79.
stack backtrace:
CPU: 0 PID: 79 Comm: qemu-system-s39 Not tainted 4.13.0+ #105
Hardware name: IBM 2964 NC9 704 (KVM/Linux)
Call Trace:
([<00000000001140b2>] show_stack+0xea/0xf0)
[<00000000008a68a4>] dump_stack+0x94/0xd8
[<0000000000134c12>] kvm_dev_ioctl+0x372/0x7a0
[<000000000038f940>] do_vfs_ioctl+0xa8/0x6c8
[<0000000000390004>] SyS_ioctl+0xa4/0xb8
[<00000000008c7a8c>] system_call+0xc4/0x27c
no locks held by qemu-system-s39/79.
We have to reset the just created users_count back to 0 to
tell the check to not trigger.
Reported-by: Stefan Haberland <sth@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Fixes: 3898da947bba ("KVM: avoid using rcu_dereference_protected")
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
virt/kvm/kvm_main.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1b3fa3f..1205d20 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -716,6 +716,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
out_err_no_srcu:
hardware_disable_all();
out_err_no_disable:
+ refcount_set(&kvm->users_count, 0);
for (i = 0; i < KVM_NR_BUSES; i++)
kfree(kvm_get_bus(kvm, i));
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
--
2.9.4
