[PATCH 5.10 037/116] KVM: eventfd: Fix false positive RCU usage warning

Greg Kroah-Hartman
2022-02-14T09:53:53Z

From: Hou Wenlong <houwenlong93@linux.alibaba.com>

[ Upstream commit 6a0c61703e3a5d67845a4b275e1d9d7bc1b5aad7 ]

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:
<TASK>
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 <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com>
Message-Id: <f98bac4f5052bad2c26df9ad50f7019e40434512.1643265976.git.houwenlong.hwl@antgroup.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 c2323c27a28b5..518cd8dc390e2 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -451,8 +451,8 @@ 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;
@@ -468,8 +468,8 @@ 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);
}
--
2.34.1