linux-kernel - Re: upstream kernel crashes

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Message-ID: <20220815174617.z4chnftzcbv6frqr@awork3.anarazel.de>
Date:   Mon, 15 Aug 2022 10:46:17 -0700
From:   Andres Freund <andres@...razel.de>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        c@...hat.com
Subject: Re: upstream kernel crashes

Hi,

On 2022-08-15 12:50:52 -0400, Michael S. Tsirkin wrote:
> On Mon, Aug 15, 2022 at 09:45:03AM -0700, Andres Freund wrote:
> > Hi,
> > 
> > On 2022-08-15 11:40:59 -0400, Michael S. Tsirkin wrote:
> > > OK so this gives us a quick revert as a solution for now.
> > > Next, I would appreciate it if you just try this simple hack.
> > > If it crashes we either have a long standing problem in virtio
> > > code or more likely a gcp bug where it can't handle smaller
> > > rings than what device requestes.
> > > Thanks!
> > 
> > I applied the below and the problem persists.
> > 
> > [...]
>
> Okay!

Just checking - I applied and tested this atop 6.0-rc1, correct? Or did you
want me to test it with the 762faee5a267 reverted? I guess what you're trying
to test if a smaller queue than what's requested you'd want to do so without
the problematic patch applied...


> And just to be 100% sure, can you try the following on top of 5.19:

> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> index 623906b4996c..6f4e54a618bc 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -208,6 +208,9 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	if (num > 1024)
> +		num = 1024;
> +
>  	info->msix_vector = msix_vec;
>  
>  	/* create the vring */
> 
> -- 

Either way, I did this, and there are no issues that I could observe. No
oopses, no broken networking. But:

To make sure it does something I added a debugging printk - which doesn't show
up. I assume this is at a point at least earlyprintk should work (which I see
getting enabled via serial)?

Greetings,

Andres Freund