From: Sean Christopherson <seanjc@google.com>
To: Yan Zhao <yan.y.zhao@intel.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com
Subject: Re: [PATCH v3] KVM: VMX: fix lockdep warning on posted intr wakeup
Date: Fri, 24 Mar 2023 16:13:37 -0700 [thread overview]
Message-ID: <ZB4uoe9WBzhG9ddU@google.com> (raw)
In-Reply-To: <20230313111022.13793-1-yan.y.zhao@intel.com>
On Mon, Mar 13, 2023, Yan Zhao wrote:
> The lock ordering after this patch are:
> - &p->pi_lock --> &rq->__lock -->
> &per_cpu(wakeup_vcpus_on_cpu_lock_out, cpu)
> - &per_cpu(wakeup_vcpus_on_cpu_lock_in, cpu) -->
> &per_cpu(wakeup_vcpus_on_cpu_lock_out, cpu)
> - &per_cpu(wakeup_vcpus_on_cpu_lock_in, cpu) --> &p->pi_lock
>
> Currently, &rq->__lock is not held in "path sched_in".
> However, if in future "path sched_in" takes &p->pi_lock or &rq->__lock,
> lockdep is able to detect and warn in that case.
>
> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
> [sean: path sched_out and path irq does not race, path sched_in does not
> take &rq->__lock]
But there's no actual deadlock, right? I have zero interest in fixing a lockdep
false positive by making functional changes to KVM. I am definitely open to making
changes to somehow let lockdep know what's going on, but complicating KVM's actual
functionality is too much.
next prev parent reply other threads:[~2023-03-24 23:13 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-13 11:10 [PATCH v3] KVM: VMX: fix lockdep warning on posted intr wakeup Yan Zhao
2023-03-24 23:13 ` Sean Christopherson [this message]
2023-03-29 1:53 ` Yan Zhao
2023-03-29 11:51 ` Paolo Bonzini
2023-03-30 9:56 ` Yan Zhao
2023-03-30 18:14 ` Sean Christopherson
2023-03-31 0:06 ` Yan Zhao
2023-04-10 17:30 ` Sean Christopherson
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