| Message ID | ab1358b84c60e6c942c270e3fe1a32bfa3177f3c.1641264282.git.houwenlong93@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: eventfd: Fix false positive RCU usage warning | expand |
On Tue, Jan 04, 2022, Hou Wenlong wrote: > Fix the following false positive warning: > [ 20.995979] ============================= > [ 20.996878] WARNING: suspicious RCU usage > [ 20.997792] 5.16.0-rc4+ #57 Not tainted > [ 20.998651] ----------------------------- > [ 20.999544] arch/x86/kvm/../../../virt/kvm/eventfd.c:484 RCU-list traversed in non-reader section!! > [ 21.001490] > [ 21.001490] other info that might help us debug this: > [ 21.001490] > [ 21.003240] > [ 21.003240] rcu_scheduler_active = 2, debug_locks = 1 > [ 21.004662] 3 locks held by fc_vcpu 0/330: > [ 21.005573] #0: ffff8884835fc0b0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x88/0x6f0 [kvm] > [ 21.007617] #1: ffffc90004c0bb68 (&kvm->srcu){....}-{0:0}, at: vcpu_enter_guest+0x600/0x1860 [kvm] > [ 21.009627] #2: ffffc90004c0c1d0 (&kvm->irq_srcu){....}-{0:0}, at: kvm_notify_acked_irq+0x36/0x180 [kvm] > [ 21.011732] > [ 21.011732] stack backtrace: > [ 21.012733] CPU: 26 PID: 330 Comm: fc_vcpu 0 Not tainted 5.16.0-rc4+ > [ 21.014189] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 > [ 21.016565] Call Trace: > [ 21.017105] <TASK> > [ 21.017591] dump_stack_lvl+0x44/0x57 > [ 21.018467] kvm_notify_acked_gsi+0x6b/0x70 [kvm] > [ 21.019533] kvm_notify_acked_irq+0x8d/0x180 [kvm] > [ 21.020616] kvm_ioapic_update_eoi+0x92/0x240 [kvm] > [ 21.021736] kvm_apic_set_eoi_accelerated+0x2a/0xe0 [kvm] > [ 21.022968] handle_apic_eoi_induced+0x3d/0x60 [kvm_intel] > [ 21.024168] vmx_handle_exit+0x19c/0x6a0 [kvm_intel] > [ 21.025255] vcpu_enter_guest+0x66e/0x1860 [kvm] > [ 21.026303] ? lock_acquire+0x27f/0x300 > [ 21.027166] ? lock_is_held_type+0xdf/0x130 > [ 21.028090] ? kvm_arch_vcpu_ioctl_run+0x438/0x7f0 [kvm] > [ 21.029286] ? kvm_arch_vcpu_ioctl_run+0x11a/0x7f0 [kvm] > [ 21.030485] kvm_arch_vcpu_ioctl_run+0x438/0x7f0 [kvm] > [ 21.031647] kvm_vcpu_ioctl+0x38a/0x6f0 [kvm] > [ 21.032647] ? __fget_files+0x156/0x220 > [ 21.033522] __x64_sys_ioctl+0x89/0xc0 > [ 21.034360] ? syscall_trace_enter.isra.18+0xea/0x260 > [ 21.035478] do_syscall_64+0x3a/0x90 > [ 21.036259] entry_SYSCALL_64_after_hwframe+0x44/0xae For future submissions, please strip the timestamps and the "? " entries, they're unnecessary noise. > Since srcu read lock is held, it's a false positive warning. Stronger phrashing should be used, this makes it sound like SRCU is held by coincidence, but kvm_unregister_irq_ack_notifier() does synchronize_srcu(&kvm->irq_srcu), i.e. irq_srcu is indeed intended protection mechansim. > Use hlist_for_each_entry_srcu() instead of hlist_for_each_entry_rcu() > as it also checkes if the right lock is held. > > Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com> Changelog nits aside, Reviewed-by: Sean Christopherson <seanjc@google.com>
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 2ad013b8bde9..59b1dd4a549e 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); }
Fix the following false positive warning: [ 20.995979] ============================= [ 20.996878] WARNING: suspicious RCU usage [ 20.997792] 5.16.0-rc4+ #57 Not tainted [ 20.998651] ----------------------------- [ 20.999544] arch/x86/kvm/../../../virt/kvm/eventfd.c:484 RCU-list traversed in non-reader section!! [ 21.001490] [ 21.001490] other info that might help us debug this: [ 21.001490] [ 21.003240] [ 21.003240] rcu_scheduler_active = 2, debug_locks = 1 [ 21.004662] 3 locks held by fc_vcpu 0/330: [ 21.005573] #0: ffff8884835fc0b0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x88/0x6f0 [kvm] [ 21.007617] #1: ffffc90004c0bb68 (&kvm->srcu){....}-{0:0}, at: vcpu_enter_guest+0x600/0x1860 [kvm] [ 21.009627] #2: ffffc90004c0c1d0 (&kvm->irq_srcu){....}-{0:0}, at: kvm_notify_acked_irq+0x36/0x180 [kvm] [ 21.011732] [ 21.011732] stack backtrace: [ 21.012733] CPU: 26 PID: 330 Comm: fc_vcpu 0 Not tainted 5.16.0-rc4+ [ 21.014189] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 21.016565] Call Trace: [ 21.017105] <TASK> [ 21.017591] dump_stack_lvl+0x44/0x57 [ 21.018467] kvm_notify_acked_gsi+0x6b/0x70 [kvm] [ 21.019533] kvm_notify_acked_irq+0x8d/0x180 [kvm] [ 21.020616] kvm_ioapic_update_eoi+0x92/0x240 [kvm] [ 21.021736] kvm_apic_set_eoi_accelerated+0x2a/0xe0 [kvm] [ 21.022968] handle_apic_eoi_induced+0x3d/0x60 [kvm_intel] [ 21.024168] vmx_handle_exit+0x19c/0x6a0 [kvm_intel] [ 21.025255] vcpu_enter_guest+0x66e/0x1860 [kvm] [ 21.026303] ? lock_acquire+0x27f/0x300 [ 21.027166] ? lock_is_held_type+0xdf/0x130 [ 21.028090] ? kvm_arch_vcpu_ioctl_run+0x438/0x7f0 [kvm] [ 21.029286] ? kvm_arch_vcpu_ioctl_run+0x11a/0x7f0 [kvm] [ 21.030485] kvm_arch_vcpu_ioctl_run+0x438/0x7f0 [kvm] [ 21.031647] kvm_vcpu_ioctl+0x38a/0x6f0 [kvm] [ 21.032647] ? __fget_files+0x156/0x220 [ 21.033522] __x64_sys_ioctl+0x89/0xc0 [ 21.034360] ? syscall_trace_enter.isra.18+0xea/0x260 [ 21.035478] do_syscall_64+0x3a/0x90 [ 21.036259] entry_SYSCALL_64_after_hwframe+0x44/0xae Since srcu read lock is held, it's a false positive warning. Use hlist_for_each_entry_srcu() instead of hlist_for_each_entry_rcu() as it also checkes if the right lock is held. Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com> --- virt/kvm/eventfd.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)