Re: [PATCH v2 3/3] PCI: Add missing bridge lock to pci_bus_lock()

[Dave Jiang <dave.jiang@intel.com>]

On 5/30/24 6:04 PM, Dan Williams wrote:
> One of the true positives that the cfg_access_lock lockdep effort
> identified is this sequence:
> 
>  WARNING: CPU: 14 PID: 1 at drivers/pci/pci.c:4886 pci_bridge_secondary_bus_reset+0x5d/0x70
>  RIP: 0010:pci_bridge_secondary_bus_reset+0x5d/0x70
>  Call Trace:
>   <TASK>
>   ? __warn+0x8c/0x190
>   ? pci_bridge_secondary_bus_reset+0x5d/0x70
>   ? report_bug+0x1f8/0x200
>   ? handle_bug+0x3c/0x70
>   ? exc_invalid_op+0x18/0x70
>   ? asm_exc_invalid_op+0x1a/0x20
>   ? pci_bridge_secondary_bus_reset+0x5d/0x70
>   pci_reset_bus+0x1d8/0x270
>   vmd_probe+0x778/0xa10
>   pci_device_probe+0x95/0x120
> 
> Where pci_reset_bus() users are triggering unlocked secondary bus
> resets. Ironically pci_bus_reset(), several calls down from
> pci_reset_bus(), uses pci_bus_lock() before issuing the reset which
> locks everything *but* the bridge itself.
> 
> For the same motivation as adding:
> 
>     bridge = pci_upstream_bridge(dev);
>     if (bridge)
>             pci_dev_lock(bridge);
> 
> ...to pci_reset_function() for the "bus" and "cxl_bus" reset cases, add
> pci_dev_lock() for @bus->self to pci_bus_lock().
> 
> Reported-by: Imre Deak <imre.deak@intel.com>
> Closes: http://lore.kernel.org/r/6657833b3b5ae_14984b29437@dwillia2-xfh.jf.intel.com.notmuch
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  drivers/pci/pci.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 8df32a3a0979..aac5daad3188 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5444,6 +5444,7 @@ static void pci_bus_lock(struct pci_bus *bus)
>  {
>  	struct pci_dev *dev;
>  
> +	pci_dev_lock(bus->self);
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		pci_dev_lock(dev);
>  		if (dev->subordinate)
> @@ -5461,6 +5462,7 @@ static void pci_bus_unlock(struct pci_bus *bus)
>  			pci_bus_unlock(dev->subordinate);
>  		pci_dev_unlock(dev);
>  	}
> +	pci_dev_unlock(bus->self);
>  }
>  
>  /* Return 1 on successful lock, 0 on contention */
> @@ -5468,6 +5470,7 @@ static int pci_bus_trylock(struct pci_bus *bus)
>  {
>  	struct pci_dev *dev;
>  
> +	pci_dev_lock(bus->self);
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		if (!pci_dev_trylock(dev))
>  			goto unlock;
> @@ -5486,6 +5489,7 @@ static int pci_bus_trylock(struct pci_bus *bus)
>  			pci_bus_unlock(dev->subordinate);
>  		pci_dev_unlock(dev);
>  	}
> +	pci_dev_unlock(bus->self);
>  	return 0;
>  }
>  
>