linux-kernel - Re: [PATCH 1/4] PCI/hotplug: Disable HPIE over reset

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Message-ID: <Z9XtUH55s9OZAPvK@wunner.de>
Date: Sat, 15 Mar 2025 22:12:48 +0100
From: Lukas Wunner <lukas@...ner.de>
To: proxy0@...amail.com
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Linux Pci <linux-pci@...r.kernel.org>,
	Guenter Roeck <groeck@...iper.net>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Rajat Jain <rajatxjain@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Stable <stable@...r.kernel.org>
Subject: Re: [PATCH 1/4] PCI/hotplug: Disable HPIE over reset

On Sat, Mar 15, 2025 at 07:57:55PM +0100, proxy0@...amail.com wrote:
> Mar 15, 2025, 9:28 PM by lukas@...ner.de:
> > After dwelling on this for a while, I'm thinking that it may re-introduce
> > the issue fixed by commit f5eff5591b8f ("PCI: pciehp: Fix AB-BA deadlock
> > between reset_lock and device_lock"):
> >
> > Looking at the second and third stack trace in its commit message,
> > down_write(reset_lock) in pciehp_reset_slot() is basically equivalent
> > to synchronize_irq() and we're holding device_lock() at that point,
> > hindering progress of pciehp_ist().
> >
> > So I think I have guided you in the wrong direction and I apologize
> > for that.
> >
> > However it seems to me that this should be solvable with the small
> > patch below.  Am I missing something?
> >
> > @Joel Mathew Thomas, could you give the below patch a spin and see
> > if it helps?
> 
> I've tested the patch series along with the additional patch provided.
> 
> Kernel: 6.14.0-rc6-00043-g3571e8b091f4-dirty-pci-hotplug-reset-fixes-eventmask-fix
> 
> Patches applied:
> - [PATCH 1/4] PCI/hotplug: Disable HPIE over reset
> - [PATCH 2/4] PCI/hotplug: Clearing HPIE for the duration of reset is enough
> - [PATCH 3/4] PCI/hotplug: reset_lock is not required synchronizing with irq thread
> - [PATCH 4/4] PCI/hotplug: Don't enable HPIE in poll mode
> - The latest patch from you:
> +	/* Ignore events masked by pciehp_reset_slot(). */
> +	events &= ctrl->slot_ctrl;
> +	if (!events)
> +		return IRQ_HANDLED;

Could you test *only* the quoted diff, i.e. without patches [1/4] - [4/4],
on top of a recent kernel?

Sorry for not having been clear about this.

I believe that patch [1/4] will re-introduce a deadlock we've
already fixed two years ago, so the small diff above seeks to
replace it with a simpler approach that will hopefully avoid
the issue as well.

Thanks,

Lukas