Re: [PATCH 2/2] pci: fix slot reset device locking

[Keith Busch <kbusch@kernel.org>]

On Wed, Jan 28, 2026 at 12:03:38PM -0600, Bjorn Helgaas wrote:
> [+cc Dan, Jinhui]
> 
> On Fri, Jan 16, 2026 at 10:41:50AM -0800, Keith Busch wrote:
> > From: Keith Busch <kbusch@kernel.org>
> > 
> > Like pci_bus_lock, pci_slot_lock needs to lock the bridge device to
> > prevent the warning:
> 
> I *think* this actually refers to pci_bus_trylock() and
> pci_slot_trylock() (not pci_bus_lock() and pci_slot_lock()), since
> that's what this patch changes?

Oh, this patch is changing both pci_slot_trylock and pci_slot_lock since
they were both missing the equivalent locks that the "bus" version of
those functions were doing.

> It's unfortunate that pci_bus_trylock() and pci_slot_trylock() are so
> similar but separate.  If there were combined, this kind of issue
> where one is fixed but the other isn't wouldn't happen.

Honestly I think the _slot versions should go away. Those don't handle
resetting a bus with multiple device's on it: only some functions get
saved and restored even though the bus reset hits all the devices. I'm
working on a fix for that, but it's more difficult than these patches.

> But what about pci_bus_lock() and pci_slot_lock()?  They are also
> almost identical, but pci_bus_lock() locks bus->self while
> pci_slot_lock() does not.  Should it?

It should, and this patch is changing pci_slot_lock() to do that.

> All these almost-but-not-quite identical paths make my head hurt ;)

I agree! And the functions that sound almost the same but work quite
different? Looking at "pci_bus_reset" vs "pci_reset_bus" :)
 
> >   pcieport 0000:e2:05.0: unlocked secondary bus reset via: pciehp_reset_slot+0x55/0xa0
> > 
> > Signed-off-by: Keith Busch <kbusch@kernel.org>
> > ---
> >  drivers/pci/pci.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 3378221c5723a..5f8b0d06a1459 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -5460,6 +5460,8 @@ static void pci_slot_lock(struct pci_slot *slot)
> >  {
> >  	struct pci_dev *dev;
> >  
> > +	if (slot->bus->self)
> > +		pci_dev_lock(slot->bus->self);
> >  	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
> >  		if (!dev->slot || dev->slot != slot)
> >  			continue;
> > @@ -5483,12 +5485,17 @@ static void pci_slot_unlock(struct pci_slot *slot)
> >  		else
> >  			pci_dev_unlock(dev);
> >  	}
> > +	if (slot->bus->self)
> > +		pci_dev_unlock(slot->bus->self);
> >  }
> >  
> >  /* Return 1 on successful lock, 0 on contention */
> >  static int pci_slot_trylock(struct pci_slot *slot)
> >  {
> > -	struct pci_dev *dev;
> > +	struct pci_dev *dev, *bridge = slot->bus->self;
> > +
> > +	if (bridge && !pci_dev_trylock(bridge))
> > +		return 0;
> >  
> >  	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
> >  		if (!dev->slot || dev->slot != slot)
> > @@ -5511,6 +5518,9 @@ static int pci_slot_trylock(struct pci_slot *slot)
> >  		else
> >  			pci_dev_unlock(dev);
> >  	}
> > +
> > +	if (bridge)
> > +		pci_dev_unlock(bridge);
> >  	return 0;
> >  }
> >  
> > -- 
> > 2.47.3
> >