linux-kernel - Re: refactor the i915 GVT support

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Date:   Thu, 26 Aug 2021 14:12:19 +0800
From:   Zhenyu Wang <zhenyuw@...ux.intel.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, Jason Gunthorpe <jgg@...dia.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...el.com>
Subject: Re: refactor the i915 GVT support

On 2021.08.20 12:56:34 -0700, Luis Chamberlain wrote:
> On Fri, Aug 20, 2021 at 04:17:24PM +0200, Christoph Hellwig wrote:
> > On Thu, Aug 19, 2021 at 04:29:29PM +0800, Zhenyu Wang wrote:
> > > I'm working on below patch to resolve this. But I met a weird issue in
> > > case when building i915 as module and also kvmgt module, it caused
> > > busy wait on request_module("kvmgt") when boot, it doesn't happen if
> > > building i915 into kernel. I'm not sure what could be the reason?
> > 
> > Luis, do you know if there is a problem with a request_module from
> > a driver ->probe routine that is probably called by a module_init
> > function itself?
> 
> Generally no, but you can easily foot yourself in the feet by creating
> cross dependencies and not dealing with them properly. I'd make sure
> to keep module initialization as simple as possible, and run whatever
> takes more time asynchronously, then use a state machine to allow
> you to verify where you are in the initialization phase or query it
> or wait for a completion with a timeout.
> 
> It seems the code in question is getting some spring cleaning, and its
> unclear where the code is I can inspect. If there's a tree somewhere I
> can take a peak I'd be happy to review possible oddities that may stick
> out.

I tried to put current patches under test here: https://github.com/intel/gvt-linux/tree/gvt-staging
The issue can be produced with CONFIG_DRM_I915=m and CONFIG_DRM_I915_GVT_KVMGT=m.

> 
> My goto model for these sorts of problems is to abstract the issue
> *outside* of the driver in question and implement new selftests to
> try to reproduce. This serves two purposes, 1) helps with testing
> 2) may allow you to see the problem more clearly.
> 

I'll see if can abstract that.

Thanks, Luis.

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