linux-kernel - Re: [PATCH v7 02/17] PCI/DPC: Log Error Source ID only when valid

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Message-ID: <20250521192352.GA1430719@bhelgaas>
Date: Wed, 21 May 2025 14:23:52 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: linux-pci@...r.kernel.org, Jon Pan-Doh <pandoh@...gle.com>,
	Karolina Stolarek <karolina.stolarek@...cle.com>,
	Weinan Liu <wnliu@...gle.com>,
	Martin Petersen <martin.petersen@...cle.com>,
	Ben Fuller <ben.fuller@...cle.com>,
	Drew Walton <drewwalton@...rosoft.com>,
	Anil Agrawal <anilagrawal@...a.com>,
	Tony Luck <tony.luck@...el.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Lukas Wunner <lukas@...ner.de>, Sargun Dhillon <sargun@...a.com>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
	Oliver O'Halloran <oohall@...il.com>,
	Kai-Heng Feng <kaihengf@...dia.com>,
	Keith Busch <kbusch@...nel.org>, Robert Richter <rrichter@....com>,
	Terry Bowman <terry.bowman@....com>,
	Shiju Jose <shiju.jose@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>
Subject: Re: [PATCH v7 02/17] PCI/DPC: Log Error Source ID only when valid

On Wed, May 21, 2025 at 10:00:35AM +0100, Jonathan Cameron wrote:
> On Tue, 20 May 2025 16:50:19 -0500
> Bjorn Helgaas <helgaas@...nel.org> wrote:
> 
> > From: Bjorn Helgaas <bhelgaas@...gle.com>
> > 
> > DPC Error Source ID is only valid when the DPC Trigger Reason indicates
> > that DPC was triggered due to reception of an ERR_NONFATAL or ERR_FATAL
> > Message (PCIe r6.0, sec 7.9.14.5).
> > 
> > When DPC was triggered by ERR_NONFATAL (PCI_EXP_DPC_STATUS_TRIGGER_RSN_NFE)
> > or ERR_FATAL (PCI_EXP_DPC_STATUS_TRIGGER_RSN_FE) from a downstream device,
> > log the Error Source ID (decoded into domain/bus/device/function).  Don't
> > print the source otherwise, since it's not valid.
> > 
> > For DPC trigger due to reception of ERR_NONFATAL or ERR_FATAL, the dmesg
> > logging changes:
> > 
> >   - pci 0000:00:01.0: DPC: containment event, status:0x000d source:0x0200
> >   - pci 0000:00:01.0: DPC: ERR_FATAL detected
> >   + pci 0000:00:01.0: DPC: containment event, status:0x000d, ERR_FATAL received from 0000:02:00.0
> > 
> > and when DPC triggered for other reasons, where DPC Error Source ID is
> > undefined, e.g., unmasked uncorrectable error:
> > 
> >   - pci 0000:00:01.0: DPC: containment event, status:0x0009 source:0x0200
> >   - pci 0000:00:01.0: DPC: unmasked uncorrectable error detected
> >   + pci 0000:00:01.0: DPC: containment event, status:0x0009: unmasked uncorrectable error detected
> > 
> > Previously the "containment event" message was at KERN_INFO and the
> > "%s detected" message was at KERN_WARNING.  Now the single message is at
> > KERN_WARNING.
> > 
> > Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > Tested-by: Krzysztof Wilczyński <kwilczynski@...nel.org>
> > Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Matches the spec conditions as far as I can tell.
> 
> I guess interesting debate on whether providing extra garbage info is
> a bug or not. Maybe a fixes tag for this one as well?

I added:

  Fixes: 26e515713342 ("PCI: Add Downstream Port Containment driver")

since it looks like we've printed the source unconditionally since the
addition of DPC:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/pcie/pcie-dpc.c?id=26e515713342#n69

> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> 
> I briefly wondered if it makes sense to have a prefix string initialized
> outside the switch with "containment event, status:%#06x:"
> made sense but it's probably not worth the effort and maybe makes it
> harder to grep for the error messages.  So in the end
> I think your code here is the best option.
> 
> Jonathan