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

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Message-ID: <20170301214120.GA30451@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 1 Mar 2017 15:41:20 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Keith Busch <keith.busch@...el.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 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?

>   To solve this, we've moved the pci release code back into the
>   unregister function and reintroduced an alive flag. This time,
>   however, the alive flag is protected by mrpc_mutex and we're very
>   careful about what happens to devices still in use (they should
>   all be released through the timeout path and an ENODEV error
>   returned to userspace; while new commands are blocked with the
>   same error).