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@xxxxxxxxxxxxxxxxx>
Changelog nits aside,
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
