linux-kernel - Re: [PATCH] PCI: hv: Only reuse existing IRTE allocation for Multi-MSI

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Date:   Tue, 16 Aug 2022 17:47:32 +0200
From:   Lorenzo Pieralisi <lpieralisi@...nel.org>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     Jeffrey Hugo <quic_jhugo@...cinc.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "robh@...nel.org" <robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "boqun.feng@...il.com" <boqun.feng@...il.com>,
        Boqun Feng <Boqun.Feng@...rosoft.com>,
        Carl Vanderlip <quic_carlv@...cinc.com>
Subject: Re: [PATCH] PCI: hv: Only reuse existing IRTE allocation for
 Multi-MSI

On Wed, Aug 10, 2022 at 09:51:23PM +0000, Dexuan Cui wrote:
> > From: Jeffrey Hugo <quic_jhugo@...cinc.com>
> > Sent: Thursday, August 4, 2022 7:22 AM
> >  ...
> > > Fixes: b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in
> > compose_msi_msg()")
> > > Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> > > Cc: Jeffrey Hugo <quic_jhugo@...cinc.com>
> > > Cc: Carl Vanderlip <quic_carlv@...cinc.com>
> > > ---
> > 
> > I'm sorry a regression has been discovered.  Right now, the issue
> > doesn't make sense to me.  I'd love to know what you find out.
> > 
> > This stopgap solution appears reasonable to me.
> > 
> > Reviewed-by: Jeffrey Hugo <quic_jhugo@...cinc.com>
> 
> Hi Lorenzo, Bjorn and all,
> Would you please take a look at the patch?

I am not very happy with this patch, it is a temporary solution to
a potential problem (or reworded: we don't know what the problem is
but we are fixing it anyway - in a way that is potentially not
related to the bug at all).

If the commit you are fixing is the problem I'd rather revert it,
waiting to understand the problem and to rework the code accordingly.

I don't think b4b77778ecc5 is essential to Hyper-V code - it is a
rework, let's fix it and repost it when it is updated through the
debugging you are carrying out. In the meantime we can revert it
to fix the issue.

Thanks,
Lorenzo