From e332b55fe79cca72451fe0b797219bd9fe6b9434 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Thu, 19 May 2022 01:49:13 -0700 Subject: [PATCH] KVM: eventfd: Fix false positive RCU usage warning The splat below can be seen when running kvm-unit-test: ============================= WARNING: suspicious RCU usage 5.18.0-rc7 #5 Tainted: G IOE ----------------------------- /home/kernel/linux/arch/x86/kvm/../../../virt/kvm/eventfd.c:80 RCU-list traversed in non-reader section!! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 4 locks held by qemu-system-x86/35124: #0: ffff9725391d80b8 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x77/0x710 [kvm] #1: ffffbd25cfb2a0b8 (&kvm->srcu){....}-{0:0}, at: vcpu_enter_guest+0xdeb/0x1900 [kvm] #2: ffffbd25cfb2b920 (&kvm->irq_srcu){....}-{0:0}, at: kvm_hv_notify_acked_sint+0x79/0x1e0 [kvm] #3: ffffbd25cfb2b920 (&kvm->irq_srcu){....}-{0:0}, at: irqfd_resampler_ack+0x5/0x110 [kvm] stack backtrace: CPU: 2 PID: 35124 Comm: qemu-system-x86 Tainted: G IOE 5.18.0-rc7 #5 Call Trace: dump_stack_lvl+0x6c/0x9b irqfd_resampler_ack+0xfd/0x110 [kvm] kvm_notify_acked_gsi+0x32/0x90 [kvm] kvm_hv_notify_acked_sint+0xc5/0x1e0 [kvm] kvm_hv_set_msr_common+0xec1/0x1160 [kvm] kvm_set_msr_common+0x7c3/0xf60 [kvm] vmx_set_msr+0x394/0x1240 [kvm_intel] kvm_set_msr_ignored_check+0x86/0x200 [kvm] kvm_emulate_wrmsr+0x4f/0x1f0 [kvm] vmx_handle_exit+0x6fb/0x7e0 [kvm_intel] vcpu_enter_guest+0xe5a/0x1900 [kvm] kvm_arch_vcpu_ioctl_run+0x16e/0xac0 [kvm] kvm_vcpu_ioctl+0x279/0x710 [kvm] __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae resampler-list is protected by irq_srcu (see kvm_irqfd_assign), so fix the false positive by using list_for_each_entry_srcu(). Signed-off-by: Wanpeng Li Message-Id: <1652950153-12489-1-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini --- virt/kvm/eventfd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 59b1dd4a549ee0..2a3ed401ce4653 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -77,7 +77,8 @@ irqfd_resampler_ack(struct kvm_irq_ack_notifier *kian) idx = srcu_read_lock(&kvm->irq_srcu); - list_for_each_entry_rcu(irqfd, &resampler->list, resampler_link) + list_for_each_entry_srcu(irqfd, &resampler->list, resampler_link, + srcu_read_lock_held(&kvm->irq_srcu)) eventfd_signal(irqfd->resamplefd, 1); srcu_read_unlock(&kvm->irq_srcu, idx);