On Mon, Apr 13, 2015 at 4:37 AM, Fam Zheng <famz@xxxxxxxxxx> wrote:
> Hi Bjorn,
>
> On Fri, 04/10 17:54, Bjorn Helgaas wrote:
>> From: Michael S. Tsirkin <mst@xxxxxxxxxx>
>>
>> d52877c7b1af ("pci/irq: let pci_device_shutdown to call pci_msi_shutdown
>> v2") disabled MSI/MSI-X at device shutdown to address a kexec problem.
>>
>> The problem is that after we disable MSI, the device may assert INTx, and
>> if the driver hasn't registered an interrupt handler for it, the interrupt
>> is never deasserted and causes a kernel hang. In particular, this was
>> observed with virtio.
>>
>> We now disable MSI/MSI-X for all devices during enumeration regardless of
>> CONFIG_PCI_MSI. This solves the kexec problem in the new kernel, not the
>> old one.
>>
>> Stop disabling MSIs at shutdown to avoid the kernel hang.
>>
>> XXX bugzilla reference, details about how the hang happens?
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=96571
>
> Please let me know if you need any further information in the bug.
Please attach a complete dmesg log. The bugzilla doesn't really have
any new information other than that you see a soft lockup. I'm trying
to connect more of the dots between a spurious interrupt and a hang or
soft lockup.
It doesn't seem right that a spurious interrupt could cause a hang or
soft lockup. I would think Linux would emit a message about the
unexpected interrupt, but would otherwise be relatively unconcerned.
So I'm trying to figure out why my assumption is wrong. Probably this
is just because I don't know much about Linux IRQ handling.
Having more details, e.g., a stacktrace fragment from a soft lockup,
can also help people connect a problem they're seeing with the
solution. It's pretty hard to google for "kernel hang," but if you
can google for a soft lockup in a specific function, that can be much
more useful.
>> [bhelgaas: changelog]
>> Reported-by: Fam Zheng <famz@xxxxxxxxxx>
>> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> CC: Yinghai Lu <yhlu.kernel.send@xxxxxxxxx>
>> CC: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
>> CC: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
>> ---
>> 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 3cb2210de553..38a602cb9fb7 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
>> /*
>>
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