linux-kernel - Re: [PATCH v6 3/5] PCI/AER: Report fatal errors of RCiEP and EP if link recoverd

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Message-ID: <aPY--DJnNam9ejpT@wunner.de>
Date: Mon, 20 Oct 2025 15:54:00 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Shuai Xue <xueshuai@...ux.alibaba.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, bhelgaas@...gle.com,
	kbusch@...nel.org, sathyanarayanan.kuppuswamy@...ux.intel.com,
	mahesh@...ux.ibm.com, oohall@...il.com, Jonathan.Cameron@...wei.com,
	terry.bowman@....com, tianruidong@...ux.alibaba.com
Subject: Re: [PATCH v6 3/5] PCI/AER: Report fatal errors of RCiEP and EP if
 link recoverd

On Mon, Oct 20, 2025 at 08:58:55PM +0800, Shuai Xue wrote:
> ??? 2025/10/20 18:10, Lukas Wunner ??????:
> > On Wed, Oct 15, 2025 at 10:41:57AM +0800, Shuai Xue wrote:
> > > +++ b/drivers/pci/pcie/err.c
> > > @@ -253,6 +254,16 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> > >   			pci_warn(bridge, "subordinate device reset failed\n");
> > >   			goto failed;
> > >   		}
> > > +
> > > +		/* Link recovered, report fatal errors of RCiEP or EP */
> > > +		if (state == pci_channel_io_frozen &&
> > > +		    (type == PCI_EXP_TYPE_ENDPOINT || type == PCI_EXP_TYPE_RC_END)) {
> > > +			aer_add_error_device(&info, dev);
> > > +			info.severity = AER_FATAL;
> > > +			if (aer_get_device_error_info(&info, 0, true))
> > > +				aer_print_error(&info, 0);
> > > +			pci_dev_put(dev);
> > > +		}
> > 
> > Where is the the pci_dev_get() to balance the pci_dev_put() here?
> 
> The corresponding pci_dev_get() is called in add_error_device(). Please
> refer to commit 60271ab044a5 ("PCI/AER: Take reference on error
> devices") which introduced this reference counting mechanism.

That is non-obvious and needs a code comment.

> > It feels awkward to leak AER-specific details into pcie_do_recovery().
> > That function is supposed to implement the flow described in
> > Documentation/PCI/pci-error-recovery.rst in a platform-agnostic way
> > so that powerpc (EEH) and s390 could conceivably take advantage of it.
> > 
> > Can you find a way to avoid this, e.g. report errors after
> > pcie_do_recovery() has concluded?
> 
> I understand your concern about keeping pcie_do_recovery()
> platform-agnostic.

The code you're adding above, with the exception of the check for
pci_channel_io_frozen, should live in a helper in aer.c.
Then you also don't need to rename add_error_device().

> I explored the possibility of reporting errors after
> recovery concludes, but unfortunately, this approach isn't feasible due
> to the recovery sequence. The issue is that most drivers'
> pci_error_handlers implement .slot_reset() which internally calls
> pci_restore_state() to restore the device's configuration space and
> state. This function also clears the device's AER status registers:
> 
>   .slot_reset()
>     => pci_restore_state()
>       => pci_aer_clear_status()

This was added in 2015 by b07461a8e45b.  The commit claims that
the errors are stale and can be ignored.  It turns out they cannot.

So maybe pci_restore_state() should print information about the
errors before clearing them?

Actually pci_restore_state() is only supposed to restore state,
as the name implies, and not clear errors.  It seems questionable
that the commit amended it to do that.

> > I'm also worried that errors are reported *during* recovery.
> > I imagine this looks confusing to a user.  The logged messages
> > should make it clear that these are errors that occurred *earlier*
> > and are reported belatedly.
> 
> You raise an excellent point about potential user confusion. The current
> aer_print_error() interface doesn't indicate that these are historical
> errors being reported belatedly. Would it be acceptable to add a
> clarifying message before calling aer_print_error()? For example:
> 
>   pci_err(dev, "Reporting error that occurred before recovery:\n");

Yes, something like that.  "Errors reported prior to reset"?  Dunno.

Thanks,

Lukas