linux-kernel - Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd

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Date:   Wed, 28 Jul 2021 21:07:14 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Juri Lelli <jlelli@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        He Zhe <zhe.he@...driver.com>, Jens Axboe <axboe@...com>
Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal()

On Wed, Jul 28 2021 at 12:21, Paolo Bonzini wrote:
> On 28/07/21 10:06, Thomas Gleixner wrote:
>> On Wed, Jul 14 2021 at 12:35, Paolo Bonzini wrote:
>> Yes, that cures it, but if you think about what this wants to prevent,
>> then having the recursion counter per CPU is at least suboptimal.
>> 
>> Something like the untested below perhaps?
>
> Yes, that works (it should just be #ifdef CONFIG_EVENTFD).

Yup and it lacks an include.

> On !PREEMPT_RT the percpu variable consumes memory while your patch uses 
> none (there are plenty of spare bits in current), but it is otherwise 
> basically the same.  On PREEMPT_RT the local_lock is certainly more 
> expensive.

Let me send a proper patch for that.

Thanks,

        tglx