Re: [PATCHv2] PCI: fix recursive device locking

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Hans, Kalle, Dave]

On Thu, Jul 11, 2024 at 12:36:50PM -0700, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> If one of the bus' devices has subordinates, the recursive call locks
> itself, so no need to lock the device before the recursion or it will
> surely deadlock.
> 
> Fixes: dbc5b5c0d268f87 ("PCI: Add missing bridge lock to pci_bus_lock()"
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Keith Busch <kbusch@kernel.org>

dbc5b5c0d268f87 was queued for the v6.11 merge window on pci/reset, so
I squashed this fix into that commit.  Thanks for the fix!

Hans, Kalle, Dave, I retained your Tested-by and Reviewed-by from
dbc5b5c0d268f87.  Please let me know if you want to update or remove
those.

> ---
> Changes from v1:
> 
>  Fixed the same recursive locking for pci_bus_trylock(),
>  pci_slot_lock(), and pci_slot_trylock()
> 
>  drivers/pci/pci.c | 33 ++++++++++++++++++---------------
>  1 file changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index df550953fa260..82b74d3f6bb1e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5488,9 +5488,10 @@ static void pci_bus_lock(struct pci_bus *bus)
>  
>  	pci_dev_lock(bus->self);
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
> -		pci_dev_lock(dev);
>  		if (dev->subordinate)
>  			pci_bus_lock(dev->subordinate);
> +		else
> +			pci_dev_lock(dev);
>  	}
>  }
>  
> @@ -5502,7 +5503,8 @@ static void pci_bus_unlock(struct pci_bus *bus)
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		if (dev->subordinate)
>  			pci_bus_unlock(dev->subordinate);
> -		pci_dev_unlock(dev);
> +		else
> +			pci_dev_unlock(dev);
>  	}
>  	pci_dev_unlock(bus->self);
>  }
> @@ -5512,16 +5514,15 @@ static int pci_bus_trylock(struct pci_bus *bus)
>  {
>  	struct pci_dev *dev;
>  
> -	pci_dev_lock(bus->self);
> +	if (!pci_dev_trylock(bus->self))
> +		return 0;
> +
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
> -		if (!pci_dev_trylock(dev))
> -			goto unlock;
>  		if (dev->subordinate) {
> -			if (!pci_bus_trylock(dev->subordinate)) {
> -				pci_dev_unlock(dev);
> +			if (!pci_bus_trylock(dev->subordinate))
>  				goto unlock;
> -			}
> -		}
> +		} else if (!pci_dev_trylock(dev))
> +			goto unlock;
>  	}
>  	return 1;
>  
> @@ -5529,7 +5530,8 @@ static int pci_bus_trylock(struct pci_bus *bus)
>  	list_for_each_entry_continue_reverse(dev, &bus->devices, bus_list) {
>  		if (dev->subordinate)
>  			pci_bus_unlock(dev->subordinate);
> -		pci_dev_unlock(dev);
> +		else
> +			pci_dev_unlock(dev);
>  	}
>  	pci_dev_unlock(bus->self);
>  	return 0;
> @@ -5563,9 +5565,10 @@ static void pci_slot_lock(struct pci_slot *slot)
>  	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
>  		if (!dev->slot || dev->slot != slot)
>  			continue;
> -		pci_dev_lock(dev);
>  		if (dev->subordinate)
>  			pci_bus_lock(dev->subordinate);
> +		else
> +			pci_dev_lock(dev);
>  	}
>  }
>  
> @@ -5591,14 +5594,13 @@ static int pci_slot_trylock(struct pci_slot *slot)
>  	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
>  		if (!dev->slot || dev->slot != slot)
>  			continue;
> -		if (!pci_dev_trylock(dev))
> -			goto unlock;
>  		if (dev->subordinate) {
>  			if (!pci_bus_trylock(dev->subordinate)) {
>  				pci_dev_unlock(dev);
>  				goto unlock;
>  			}
> -		}
> +		} else if (!pci_dev_trylock(dev))
> +			goto unlock;
>  	}
>  	return 1;
>  
> @@ -5609,7 +5611,8 @@ static int pci_slot_trylock(struct pci_slot *slot)
>  			continue;
>  		if (dev->subordinate)
>  			pci_bus_unlock(dev->subordinate);
> -		pci_dev_unlock(dev);
> +		else
> +			pci_dev_unlock(dev);
>  	}
>  	return 0;
>  }
> -- 
> 2.43.0
>