linux-kernel - Re: kernel/rcu/tree.c:1031 rcu_irq_enter() invoked with irqs enabled!!!!

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Date:   Wed, 26 Apr 2017 16:29:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        Jan Kara <jack@...e.cz>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>, kvm@...r.kernel.org
Subject: Re: kernel/rcu/tree.c:1031 rcu_irq_enter() invoked with irqs
 enabled!!!!



On 26/04/2017 16:18, Radim Krčmář wrote:
>> OK, but looking at the stack trace, this has nothing to do with ext4. The
>> problem seems to be in KVM - relevant CCs added.
> The path begins with async_page_fault interrupt gate and the hardware
> should clear the interrupt flag before executing it.  I don't see a
> change that would break the assumption that interrupts are disabled ...

native_safe_halt enables interrupts.  I think this is it:

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 14f65a5f938e..2a7835932b71 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -161,8 +161,8 @@ void kvm_async_pf_task_wait(u32 token)
 			 */
 			rcu_irq_exit();
 			native_safe_halt();
-			rcu_irq_enter();
 			local_irq_disable();
+			rcu_irq_enter();
 		}
 	}
 	if (!n.halted)

Paolo