linux-kernel - RE: [PATCH RFC] pci: report surprise removal events

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Message-ID:
 <CY8PR12MB7195F2F2900BAEA69F5431E9DC46A@CY8PR12MB7195.namprd12.prod.outlook.com>
Date: Mon, 30 Jun 2025 04:07:55 +0000
From: Parav Pandit <parav@...dia.com>
To: Keith Busch <kbusch@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>
CC: Lukas Wunner <lukas@...ner.de>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"virtualization@...ts.linux.dev" <virtualization@...ts.linux.dev>,
	"stefanha@...hat.com" <stefanha@...hat.com>, "alok.a.tiwari@...cle.com"
	<alok.a.tiwari@...cle.com>
Subject: RE: [PATCH RFC] pci: report surprise removal events


> From: Keith Busch <kbusch@...nel.org>
> Sent: 30 June 2025 05:10 AM
> 
> On Sun, Jun 29, 2025 at 01:28:08PM -0400, Michael S. Tsirkin wrote:
> > On Sun, Jun 29, 2025 at 03:36:27PM +0200, Lukas Wunner wrote:
> > > On Sat, Jun 28, 2025 at 02:58:49PM -0400, Michael S. Tsirkin wrote:
> > >
> > > 1/ The device_lock() will reintroduce the issues solved by 74ff8864cc84.
> >
> > I see. What other way is there to prevent dev->driver from going away,
> > though? I guess I can add a new spinlock and take it both here and
> > when
> > dev->driver changes? Acceptable?
> 
> You're already holding the pci_bus_sem here, so the final device 'put'
> can't have been called yet, so the device is valid and thread safe in this
> context. I think maintaining the desired lifetime of the instantiated driver is
> just a matter of reference counting within your driver.
> 
> Just a thought on your patch, instead of introducing a new callback, you could
> call the existing '->error_detected()' callback with the previously set
> 'pci_channel_io_perm_failure' status. That would totally work for nvme to
> kick its cleanup much quicker than the blk_mq timeout handling we currently
> rely on for this scenario.

error_detected() callback is also called while holding the device_lock() by report_error_detected().
So when remove() callback is ongoing for graceful removal and driver is waiting for the request completions,

If the error_detected() will be stuck on device lock.

We likely need async notification from driver kernel core without holding the device lock, so driver can initiate cleanup in this corner case.