On Wed, Oct 19, 2011 at 5:02 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Mon, Oct 17, 2011 at 12:46 PM, Eric W. Biederman
> <ebiederm@xxxxxxxxxxxx> wrote:
>>
>> I traced a nasty kexec on panic boot failure to the fact that we had
>> screaming msi interrupts and we were not disabling the msi messages at
>> kernel startup. The booting kernel had not enabled those interupts so
>> was not prepared to handle them.
>>
>> I can see no reason why we would ever want to leave the msi interrupts
>> enabled at boot if something else has enabled those interrupts. The pci
>> spec specifies that msi interrupts should be off by default. Drivers
>> are expected to enable the msi interrupts if they want to use them. Our
>> interrupt handling code reprograms the interrupt handlers at boot and
>> will not be be able to do anything useful with an unexpected interrupt.
>>
>> This patch applies cleanly all of the way back to 2.6.32 where I noticed
>> the problem.
>>
>> Cc: stable@xxxxxxxxxx
>>
>> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
>> ---
>> drivers/pci/msi.c | 10 ++++++++++
>> 1 files changed, 10 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index 2f10328..e174982 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -869,5 +869,15 @@ EXPORT_SYMBOL(pci_msi_enabled);
>>
>> void pci_msi_init_pci_dev(struct pci_dev *dev)
>> {
>> + int pos;
>> INIT_LIST_HEAD(&dev->msi_list);
>> +
>> + /* Disable the msi hardware to avoid screaming interrupts
>> + * during boot. This is the power on reset default so
>> + * usually this should be a noop.
>> + */
>> + pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
>> + if (pos)
>> + msi_set_enable(dev, pos, 0);
>> + msix_set_enable(dev, 0);
>> }
>
> We only build msi.o if CONFIG_PCI_MSI=y, but don't you want to disable
> these even if the new kernel has CONFIG_PCI_MSI=n?
Since problems like this are so nasty to debug, maybe it'd be worth a
note in dmesg if we found MSI enabled? I guess I don't know exactly
what we'd do with the information, but sometimes we can't predict in
advance what things are useful.
Bjorn
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