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KVM: avoid using rcu_dereference_protected

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During teardown, accesses to memslots and buses are using
rcu_dereference_protected with an always-true condition because
these accesses are done outside the usual mutexes.  This
is because the last reference is gone and there cannot be any
concurrent modifications, but rcu_dereference_protected is
ugly and unobvious.

Instead, check the refcount in kvm_get_bus and __kvm_memslots.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
This commit is contained in:
Paolo Bonzini
2017-08-02 17:55:54 +02:00
committed by Radim Krčmář
parent ebd28fcb55
commit 3898da947b
2 changed files with 8 additions and 9 deletions
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6
include/linux/kvm_host.h
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@@ -477,7 +477,8 @@ struct kvm {
static inline struct kvm_io_bus *kvm_get_bus(struct kvm *kvm, enum kvm_bus idx)
{
return srcu_dereference_check(kvm->buses[idx], &kvm->srcu,
lockdep_is_held(&kvm->slots_lock));
lockdep_is_held(&kvm->slots_lock) ||
!refcount_read(&kvm->users_count));
}
static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
@@ -570,7 +571,8 @@ void kvm_put_kvm(struct kvm *kvm);
static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id)
{
return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu,
lockdep_is_held(&kvm->slots_lock));
lockdep_is_held(&kvm->slots_lock) ||
!refcount_read(&kvm->users_count));
}
static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)