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

From: Johan Hovold <johan@kernel.org>
To: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: "Marc Zyngier" <maz@kernel.org>,
	"Bjorn Helgaas" <helgaas@kernel.org>,
	"Pali Rohár" <pali@kernel.org>,
	"Johan Hovold" <johan+linaro@kernel.org>,
	"Kishon Vijay Abraham I" <kishon@ti.com>,
	"Xiaowei Song" <songxiaowei@hisilicon.com>,
	"Binghui Wang" <wangbinghui@hisilicon.com>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Ryder Lee" <ryder.lee@mediatek.com>,
	"Jianjun Wang" <jianjun.wang@mediatek.com>,
	linux-pci@vger.kernel.org, "Krzysztof Wilczyński" <kw@linux.com>,
	"Ley Foon Tan" <ley.foon.tan@intel.com>,
	linux-kernel@vger.kernel.org
Subject: Re: Why set .suppress_bind_attrs even though .remove() implemented?
Date: Wed, 28 Sep 2022 08:36:15 +0200	[thread overview]
Message-ID: <YzPrX2UBfv/eXyjs@hovoldconsulting.com> (raw)
In-Reply-To: <YzMWbmWWul1AhpuR@lpieralisi>

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