linux-kernel - Re: Why set .suppress_bind_attrs even though .remove() implemented?

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Message-ID: <YzPrX2UBfv/eXyjs@hovoldconsulting.com>
Date:   Wed, 28 Sep 2022 08:36:15 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Lorenzo Pieralisi <lpieralisi@...nel.org>
Cc:     Marc Zyngier <maz@...nel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        Pali Rohár <pali@...nel.org>,
        Johan Hovold <johan+linaro@...nel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Xiaowei Song <songxiaowei@...ilicon.com>,
        Binghui Wang <wangbinghui@...ilicon.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        linux-pci@...r.kernel.org,
        Krzysztof Wilczyński <kw@...ux.com>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: Why set .suppress_bind_attrs even though .remove() implemented?

On Tue, Sep 27, 2022 at 05:27:42PM +0200, Lorenzo Pieralisi wrote:
> On Mon, Jul 25, 2022 at 06:35:27PM +0100, Marc Zyngier wrote:
> 
> [...]
> 
> > > That is precisely the way I've been testing it and everything appears
> > > to be tore down as it should.
> > >
> > > And a PCI driver that has been unbound should have released its
> > > resources, or that's a driver bug. Right?
> > 
> > But that's the thing: you can easily remove part of the infrastructure
> > without the endpoint driver even noticing. It may not happen in your
> > particular case if removing the RC driver will also nuke the endpoints
> > in the process, but I can't see this is an absolute guarantee. The
> > crash pointed to by an earlier email is symptomatic of it.
> > 
> > > And for the OF INTx case you mentioned earlier, aren't those mapped by
> > > PCI core and could in theory be released by core as well?
> > 
> > Potentially, though I haven't tried to follow the life cycle of those.
> > The whole thing is pretty fragile, and this sort of resource is rarely
> > expected to be removed...
> 
> This made me notice that we don't undo the actions (ie bridge->map_irq())
> executed in pci_assign_irq() in pci_device_remove(); I don't think this
> can be right and that's already a candidate for a fix.

There's an inherent asymmetry here as a legacy interrupt can be used by
more than one device. It is mapped on first use as each user calls
->map_irq() but can only be disposed when the final user is gone as I
mentioned here:

	https://lore.kernel.org/all/Yt+6azfwd%2FLuMzoG@hovoldconsulting.com/

> It is not necessarily related to this thread topic, though I believe,
> in an _ideal_ world, removing a bridge should guarantee that all
> the downstream devices (ie drivers) had a chance of freeing/disposing
> the resources they allocated. This in theory; I totally understand
> Marc's point of view here and we should make up our mind about what
> we want to do on host bridge removal policy - this will take me more
> time to get to the bottom of it.

Johan