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    SubjectRe: upstream kernel crashes
    Hi,

    On 2022-08-15 16:21:51 -0400, Michael S. Tsirkin wrote:
    > On Mon, Aug 15, 2022 at 10:46:17AM -0700, Andres Freund wrote:
    > > 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...
    > >
    > >
    > > 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)?
    > >

    > Sorry if I was unclear. I wanted to know whether the change somehow
    > exposes a driver bug or a GCP bug. So what I wanted to do is to test
    > this patch on top of *5.19*, not on top of the revert.

    Right, the 5.19 part was clear, just the earlier test:

    > > > > 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
    > > > > > Thanks!

    I wasn't sure about.

    After I didn't see any effect on 5.19 + your patch, I grew a bit suspicious
    and added the printks.


    > Yes I think printk should work here.

    The reason the debug patch didn't change anything, and that my debug printk
    didn't show, is that gcp uses the legacy paths...

    If there were a bug in the legacy path, it'd explain why the problem only
    shows on gcp, and not in other situations.

    I'll queue testing the legacy path with the equivalent change.

    - Andres


    Greetings,

    Andres Freund

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