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Message-ID: <4opfq7hcowqwmz2hzpfcu3icx3z6ce4vmn6pkaeeqxnclgvjd6@x7lyji2owgae>
Date: Tue, 30 May 2023 18:11:58 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Mike Christie <michael.christie@...cle.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
syzbot <syzbot+d0d442c22fa8db45ff0e@...kaller.appspotmail.com>, jasowang@...hat.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com,
virtualization@...ts.linux-foundation.org, stefanha@...hat.com
Subject: Re: [syzbot] [kvm?] [net?] [virt?] general protection fault in
vhost_work_queue
On Tue, May 30, 2023 at 11:01:11AM -0500, Mike Christie wrote:
>On 5/30/23 10:58 AM, Mike Christie wrote:
>> On 5/30/23 8:44 AM, Stefano Garzarella wrote:
>>>
>>> From a first glance, it looks like an issue when we call vhost_work_queue().
>>> @Mike, does that ring any bells since you recently looked at that code?
>>
>> I see the bug. needed to have set the dev->worker after setting worker->vtsk
Yes, I came to the same conclusion (see my email sent at the same time
:-).
>> like below:
>>
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index a92af08e7864..7bd95984a501 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -564,7 +564,6 @@ static int vhost_worker_create(struct vhost_dev *dev)
>> if (!worker)
>> return -ENOMEM;
>>
>> - dev->worker = worker;
>> worker->kcov_handle = kcov_common_handle();
>> init_llist_head(&worker->work_list);
>> snprintf(name, sizeof(name), "vhost-%d", current->pid);
>> @@ -576,6 +575,7 @@ static int vhost_worker_create(struct vhost_dev *dev)
>> }
>>
>> worker->vtsk = vtsk;
>
>Shoot, oh wait, I think I needed a smp_wmb to always make sure worker->vtask
>is set before dev->worker or vhost_work_queue could still end up seeing
>dev->worker set before worker->vtsk right?
But should we pair smp_wmb() with an smp_rmb() wherever we check
dev->worker?
Thanks,
Stefano
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