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Subject: Re: linux-next: OOPS at bot time
From: Ben Hutchings <bhutchings@solarflare.com>
To: Stephen Rothwell <sfr@canb.auug.org.au>
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Date: Fri, 23 Jul 2010 02:19:45 +0100
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	LKML <linux-kernel@vger.kernel.org>,
	Jesse Barnes <jbarnes@virtuousgeek.org>
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On Fri, 2010-07-23 at 10:22 +1000, Stephen Rothwell wrote:
> Hi all,
> 
> My Power7 boot test paniced like this: (next-20100722)
> 
> %GQLogic Fibre Channel HBA Driver: 8.03.03-k0
> qla2xxx 0002:01:00.2: enabling device (0144 -> 0146)
> qla2xxx 0002:01:00.2: Found an ISP8001, irq 35, iobase 0xd000080080014000
> ------------[ cut here ]------------
> kernel BUG at drivers/pci/msi.c:205!
[...]
> Call Trace:
> [c00000000278b270] [c000000000048d9c] .rtas_setup_msi_irqs+0x1d8/0x254 (unreliable)
> [c00000000278b360] [c00000000002a9cc] .arch_setup_msi_irqs+0x34/0x4c
> [c00000000278b3e0] [c0000000002fd3fc] .pci_enable_msix+0x49c/0x4ac
[...]
> That line number is this:
> 
> 	BUG_ON(!(entry->msg.address_hi | entry->msg.address_lo |
> 		 entry->msg.data));
> 
> in read_msi_msg_desc().  That BUG_ON was added by commit
> 2ca1af9aa3285c6a5f103ed31ad09f7399fc65d7 ("PCI: MSI: Remove unsafe and
> unnecessary hardware access") from the pci tree.

I wanted to assert that read_msi_msg_desc() is only used to update
MSI/MSI-X descriptors that have already been generated by Linux.  It
looks like you found an exception.

We could make read_msi_msg() fall back to reading from the hardware, but
I think that what the pSeries code is trying to do - save an MSI message
generated by firmware - is different from what the other callers want.
Instead we could add:

void save_msi_msg(unsigned int irq)
{
	struct irq_desc *desc = irq_to_desc(irq);
	struct msi_desc *entry = get_irq_desc_msi(desc);
	struct msi_msg *msg = &entry->msg;

	/* ...followed by the old implementation of read_msi_msg_desc() */
}

Possibly conditional on something like CONFIG_ARCH_NEEDS_SAVE_MSI_MSG.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.