Re: [PATCH] PCI: Make PCI cfg_access_lock lockdep key a singleton

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

On 5/28/24 4:22 PM, Dan Williams wrote:
> The new lockdep annotation for cfg_access_lock naively registered a new
> key per device. This is overkill and leads to warnings on hash
> collisions at dynamic registration time:
> 
>  WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:1226 lockdep_register_key+0xb0/0x240
>  RIP: 0010:lockdep_register_key+0xb0/0x240
>  [..]
>  Call Trace:
>   <TASK>
>   ? __warn+0x8c/0x190
>   ? lockdep_register_key+0xb0/0x240
>   ? report_bug+0x1f8/0x200
>   ? handle_bug+0x3c/0x70
>   ? exc_invalid_op+0x18/0x70
>   ? asm_exc_invalid_op+0x1a/0x20
>   ? lockdep_register_key+0xb0/0x240
>   pci_device_add+0x14b/0x560
>   ? pci_setup_device+0x42e/0x6a0
>   pci_scan_single_device+0xa7/0xd0
>   p2sb_scan_and_cache_devfn+0xc/0x90
>   p2sb_fs_init+0x15f/0x170
> 
> Switch to a shared static key for all instances.
> 
> Fixes: 7e89efc6e9e4 ("PCI: Lock upstream bridge for pci_reset_function()")
> Reported-by: Jani Saarinen <jani.saarinen@intel.com>
> Closes: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_14834/bat-apl-1/boot0.txt
> 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>

> ---
> Hi Bjorn,
> 
> One more fallout from the cfg_access_lock lockdep annotation. This one
> still wants a Tested-by from Jani before merging, but wanted to make you
> aware of it in case similar reports make their way to you in the
> meantime.
> 
>  drivers/pci/probe.c |    7 ++++---
>  include/linux/pci.h |    1 -
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 8e696e547565..15168881ec94 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2533,6 +2533,8 @@ static void pci_set_msi_domain(struct pci_dev *dev)
>  	dev_set_msi_domain(&dev->dev, d);
>  }
>  
> +static struct lock_class_key cfg_access_key;
> +
>  void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
>  {
>  	int ret;
> @@ -2546,9 +2548,8 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
>  	dev->dev.dma_mask = &dev->dma_mask;
>  	dev->dev.dma_parms = &dev->dma_parms;
>  	dev->dev.coherent_dma_mask = 0xffffffffull;
> -	lockdep_register_key(&dev->cfg_access_key);
> -	lockdep_init_map(&dev->cfg_access_lock, dev_name(&dev->dev),
> -			 &dev->cfg_access_key, 0);
> +	lockdep_init_map(&dev->cfg_access_lock, "&dev->cfg_access_lock",
> +			 &cfg_access_key, 0);
>  
>  	dma_set_max_seg_size(&dev->dev, 65536);
>  	dma_set_seg_boundary(&dev->dev, 0xffffffff);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index fb004fd4e889..5bece7fd11f8 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -413,7 +413,6 @@ struct pci_dev {
>  	struct resource driver_exclusive_resource;	 /* driver exclusive resource ranges */
>  
>  	bool		match_driver;		/* Skip attaching driver */
> -	struct lock_class_key cfg_access_key;
>  	struct lockdep_map cfg_access_lock;
>  
>  	unsigned int	transparent:1;		/* Subtractive decode bridge */
>