From 021086e383fa408a219f6c6541b37f495f59d576 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Wed, 13 Sep 2017 14:17:22 +0200 Subject: [PATCH] KVM: fix rcu warning on VM_CREATE errors MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Christian Borntraeger Fixes: 3898da947bba ("KVM: avoid using rcu_dereference_protected") Cc: Paolo Bonzini Reviewed-by: David Hildenbrand Signed-off-by: Radim Krčmář --- 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 6ed1c2021198..2d7df5cc955b 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -674,6 +674,7 @@ out_err_no_irq_srcu: 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++) -- 2.20.1