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([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.googlemail.com with ESMTPSA id w17sm9076036edd.18.2022.02.10.08.41.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Feb 2022 08:41:05 -0800 (PST) Message-ID: <6f3d4ed7-f3c1-7c06-d5cf-1bd824731e43@redhat.com> Date: Thu, 10 Feb 2022 17:41:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH MANUALSEL 5.16 1/8] KVM: eventfd: Fix false positive RCU usage warning Content-Language: en-US To: Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Hou Wenlong , Sean Christopherson , kvm@vger.kernel.org References: <20220209185635.48730-1-sashal@kernel.org> From: Paolo Bonzini In-Reply-To: <20220209185635.48730-1-sashal@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/9/22 19:56, Sasha Levin wrote: > From: Hou Wenlong > > [ Upstream commit 6a0c61703e3a5d67845a4b275e1d9d7bc1b5aad7 ] Acked-by: Paolo Bonzini Paolo > Fix the following false positive warning: > ============================= > WARNING: suspicious RCU usage > 5.16.0-rc4+ #57 Not tainted > ----------------------------- > arch/x86/kvm/../../../virt/kvm/eventfd.c:484 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > rcu_scheduler_active = 2, debug_locks = 1 > 3 locks held by fc_vcpu 0/330: > #0: ffff8884835fc0b0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x88/0x6f0 [kvm] > #1: ffffc90004c0bb68 (&kvm->srcu){....}-{0:0}, at: vcpu_enter_guest+0x600/0x1860 [kvm] > #2: ffffc90004c0c1d0 (&kvm->irq_srcu){....}-{0:0}, at: kvm_notify_acked_irq+0x36/0x180 [kvm] > > stack backtrace: > CPU: 26 PID: 330 Comm: fc_vcpu 0 Not tainted 5.16.0-rc4+ > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 > Call Trace: > > dump_stack_lvl+0x44/0x57 > kvm_notify_acked_gsi+0x6b/0x70 [kvm] > kvm_notify_acked_irq+0x8d/0x180 [kvm] > kvm_ioapic_update_eoi+0x92/0x240 [kvm] > kvm_apic_set_eoi_accelerated+0x2a/0xe0 [kvm] > handle_apic_eoi_induced+0x3d/0x60 [kvm_intel] > vmx_handle_exit+0x19c/0x6a0 [kvm_intel] > vcpu_enter_guest+0x66e/0x1860 [kvm] > kvm_arch_vcpu_ioctl_run+0x438/0x7f0 [kvm] > kvm_vcpu_ioctl+0x38a/0x6f0 [kvm] > __x64_sys_ioctl+0x89/0xc0 > do_syscall_64+0x3a/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Since kvm_unregister_irq_ack_notifier() does synchronize_srcu(&kvm->irq_srcu), > kvm->irq_ack_notifier_list is protected by kvm->irq_srcu. In fact, > kvm->irq_srcu SRCU read lock is held in kvm_notify_acked_irq(), making it > a false positive warning. So use hlist_for_each_entry_srcu() instead of > hlist_for_each_entry_rcu(). > > Reviewed-by: Sean Christopherson > Signed-off-by: Hou Wenlong > Message-Id: > Signed-off-by: Paolo Bonzini > Signed-off-by: Sasha Levin > --- > virt/kvm/eventfd.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 2ad013b8bde96..59b1dd4a549ee 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -463,8 +463,8 @@ bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin) > idx = srcu_read_lock(&kvm->irq_srcu); > gsi = kvm_irq_map_chip_pin(kvm, irqchip, pin); > if (gsi != -1) > - hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list, > - link) > + hlist_for_each_entry_srcu(kian, &kvm->irq_ack_notifier_list, > + link, srcu_read_lock_held(&kvm->irq_srcu)) > if (kian->gsi == gsi) { > srcu_read_unlock(&kvm->irq_srcu, idx); > return true; > @@ -480,8 +480,8 @@ void kvm_notify_acked_gsi(struct kvm *kvm, int gsi) > { > struct kvm_irq_ack_notifier *kian; > > - hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list, > - link) > + hlist_for_each_entry_srcu(kian, &kvm->irq_ack_notifier_list, > + link, srcu_read_lock_held(&kvm->irq_srcu)) > if (kian->gsi == gsi) > kian->irq_acked(kian); > }