linux-kernel - Re: [PATCH v5 0/4] New Microsemi PCI Switch Management Driver

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Message-ID: <20170301222651.GA14852@localhost.localdomain>
Date:   Wed, 1 Mar 2017 17:26:51 -0500
From:   Keith Busch <keith.busch@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Myron Stowe <myron.stowe@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Jonathan Corbet <corbet@....net>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Wei Zhang <wzhang@...com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        Stephen Bates <stephen.bates@...rosemi.com>,
        linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/4] New Microsemi PCI Switch Management Driver

On Wed, Mar 01, 2017 at 03:41:20PM -0600, Bjorn Helgaas wrote:
> On Sat, Feb 25, 2017 at 11:53:13PM -0700, Logan Gunthorpe wrote:
> > Changes since v4:
> > 
> > * Turns out pushing the pci release code into the device release
> >   function didn't work as I would have liked. If you try to unbind the
> >   device with an instance open, then you hit a kernel bug at
> >   drivers/pci/msi.c:371. (This didn't occur in v3.)
> 
> This is in free_msi_irqs():
> 
>   368    for_each_pci_msi_entry(entry, dev)
>   369            if (entry->irq)
>   370                    for (i = 0; i < entry->nvec_used; i++)
>   371                            BUG_ON(irq_has_action(entry->irq + i));
> 
> I don't think this is indicating a bug in the PCI core (although I do
> think a BUG_ON() here is an excessive response).  I think it's an
> indication that the driver didn't disconnect its ISR.  Without more
> details of the failure it's hard to tell if the BUG_ON is a symptom of
> a problem in the driver or what.
> 
> An "alive" flag feels racy, and I can't tell if it's really the best
> way to deal with this, or if it's just avoiding the issue.  There must
> be other drivers with the same cleanup issue -- do they handle it the
> same way?

I think this is from using the managed device resource API to request the
irq actions. The scope of the resource used to be tied to the pci_dev's
dev, but now it's the new switchec class dev, which has a different
lifetime while open references exist, so it's not releasing the irq's.

One thing about the BUG_ON that is confusing me is how it's getting
to free_msi_irq's BUG in v4 or v5. I don't see any part releasing the
allocated ones. Maybe the devres API is harder to use than having the
driver manage all the resources...