Re: [PATCH v5 04/10] pci: don't disable msi/msix at shutdown

[Bjorn Helgaas <bhelgaas@google.com>]

Hi Michael,

On Sun, Mar 29, 2015 at 05:04:11PM +0200, Michael S. Tsirkin wrote:
> This partially reverts commit d52877c7b1afb8c37ebe17e2005040b79cb618b0:
> 	"pci/irq: let pci_device_shutdown to call pci_msi_shutdown v2"
> 
> It's un-necessary now that we disable msi at start, and it actually
> turns out to cause problems: some device drivers don't register a level
> interrupt handler when they detect msi/msix capability, switching off
> msi while device is going causes device to assert a level interrupt
> which is never de-asserted, causing a kernel hang.
> 
> In particular, this was observed with virtio.

I'm not questioning that this hang happens, but would you mind outlining
*how* it happens in a little more detail?  I'm not an IRQ expert, so I
expected an "irq %d: nobody cared" message or something similar.  It seems
like a kernel hang is a pretty severe way to deal with an unexpected
interrupt.

Is virtio the only way the hang could happen, or is it just coincidence
that it was involved?

It'd be really nice if we could reference the bug report here.  I think you
said the original report was private.  Can we open a kernel.org bugzilla
that contains just the public information?

> Cc: Yinghai Lu <yhlu.kernel.send@gmail.com>
> Cc: Ulrich Obergfell <uobergfe@redhat.com>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Reported-by: Fam Zheng <famz@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  drivers/pci/pci-driver.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 3cb2210..38a602c 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -450,8 +450,6 @@ static void pci_device_shutdown(struct device *dev)
>  
>  	if (drv && drv->shutdown)
>  		drv->shutdown(pci_dev);
> -	pci_msi_shutdown(pci_dev);
> -	pci_msix_shutdown(pci_dev);
>  
>  #ifdef CONFIG_KEXEC
>  	/*
> -- 
> MST
>