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From: Paolo Bonzini <pbonzini@redhat.com>
To: Hillf Danton <hdanton@sina.com>
Cc: Jason Wang <jasowang@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Juri Lelli <jlelli@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>, He Zhe <zhe.he@windriver.com>
Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal()
Date: Fri, 16 Jul 2021 09:59:15 +0200	[thread overview]
Message-ID: <8759e324-418b-493a-adee-236738cc3a4f@redhat.com> (raw)
In-Reply-To: <20210716075539.2376-1-hdanton@sina.com>

On 16/07/21 09:55, Hillf Danton wrote:
> On Fri, 16 Jul 2021 08:54:58 +0200 Paolo Bonzini wrote:
>> On 16/07/21 04:06, Hillf Danton wrote:
>>>> With the patch:
>>>> 	- no warn
>>>> 	- continue using the VM normally...
>>> Well with the patch applied, the VM works fine without the stuff protected
>>> by the spin_lock_irqsave(), then without the patch why simply printing a
>>> warning makes the VM dumb, given the warning is there actually also
>>> preventing you from touching the lock.
>>
>> If the warning is triggered, eventfd_signal will not do the wakeup.
> 
> [I am assuming we are not talking about the deadlock in the comment.]
> 
> No preemption occured without the warning printed.
> Why will the wakeup behavior change without peemption?

Sorry, I don't follow.  What I'm saying is that without the patch:

* the warning only occurs if preemption occurs during the 
spin_lock_irqsave critical section (and therefore it can only occur in 
PREEMPT_RT kernels)

* the warning causes an early return 0 that messes up the VM's networking

Paolo


  parent reply	other threads:[~2021-07-16  7:59 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14  8:01 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal() Daniel Bristot de Oliveira
2021-07-14  8:10 ` Paolo Bonzini
2021-07-14  9:23   ` Jason Wang
2021-07-14 10:35     ` Paolo Bonzini
2021-07-14 10:41       ` Michael S. Tsirkin
2021-07-14 10:44         ` Paolo Bonzini
2021-07-14 12:20       ` Daniel Bristot de Oliveira
2021-07-15  4:14       ` Jason Wang
2021-07-15  5:58         ` Paolo Bonzini
2021-07-15  6:45           ` Jason Wang
2021-07-15  8:22       ` Daniel Bristot de Oliveira
2021-07-15  8:44         ` He Zhe
2021-07-15  9:51           ` Paolo Bonzini
2021-07-15 10:10             ` He Zhe
2021-07-15 11:05               ` Paolo Bonzini
2021-07-16  2:26                 ` Jason Wang
2021-07-16  2:43                   ` He Zhe
2021-07-16  2:46                     ` Jason Wang
2021-07-15  9:46         ` Paolo Bonzini
2021-07-15 12:34           ` Daniel Bristot de Oliveira
     [not found]       ` <20210715102249.2205-1-hdanton@sina.com>
2021-07-15 12:31         ` Daniel Bristot de Oliveira
     [not found]         ` <20210716020611.2288-1-hdanton@sina.com>
2021-07-16  6:54           ` Paolo Bonzini
     [not found]           ` <20210716075539.2376-1-hdanton@sina.com>
2021-07-16  7:59             ` Paolo Bonzini [this message]
     [not found]             ` <20210716093725.2438-1-hdanton@sina.com>
2021-07-16 11:55               ` Paolo Bonzini
2021-07-18 12:42                 ` Hillf Danton
2021-07-19 15:38                   ` Paolo Bonzini
2021-07-21  7:04                     ` Hillf Danton
2021-07-21  7:25                       ` Thomas Gleixner
2021-07-21 10:11                         ` Hillf Danton
2021-07-21 10:59                           ` Paolo Bonzini
2021-07-22  5:58                             ` Hillf Danton
2021-07-23  2:23                             ` Hillf Danton
2021-07-23  7:59                               ` Paolo Bonzini
2021-07-23  9:48                                 ` Hillf Danton
2021-07-23 10:56                                   ` Paolo Bonzini
2021-07-24  4:33                                     ` Hillf Danton
2021-07-26 11:03                                       ` Paolo Bonzini
2021-07-28  8:06       ` Thomas Gleixner
2021-07-28 10:21         ` Paolo Bonzini
2021-07-28 19:07           ` Thomas Gleixner
2021-07-29 11:01             ` [PATCH] eventfd: Make signal recursion protection a task bit Thomas Gleixner
2021-07-29 14:32               ` Daniel Bristot de Oliveira
2021-07-29 19:23               ` Daniel Bristot de Oliveira
2021-08-26  7:03               ` Jason Wang
2021-08-27 23:41               ` [tip: sched/core] " tip-bot2 for Thomas Gleixner

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