Re: [PATCH] pci: avoid dead lock between device reset and sriov disable

[Bjorn Helgaas]

[+cc Don, Jason, Leon, just FYI]

On Mon, Apr 04, 2022 at 02:25:39PM +0800, Jay Zhou wrote:
> Call trace of PF SRIOV disable:
> sriov_numvfs_store
>   device_lock <----------------- (1) get the device lock
>     ->sriov_configure # e.g. vfio_pci_sriov_configure
>       sriov_disable
>         pci_cfg_access_lock <--- (4) wait dev->block_cfg_access to be 0
> 
> Call trace of PF reset:
> reset_store
>   pci_reset_function
>     pci_dev_lock
>       pci_cfg_access_lock <----- (2) set dev->block_cfg_access = 1
>       device_lock <------------- (3) want to get the device lock
> 
> These two oprations would wait for each other forever if the
> code execution sequence is (1)(2)(3)(4).
> 
> Let's get the device lock and then the config access lock in
> pci_dev_lock().
> 
> Signed-off-by: Jay Zhou <jianjay.zhou@xxxxxxxxxx>

Thanks, I (finally) applied Yicong's identical patch from a year ago
to pci/virtualization for v5.19, with a commit log combined and
adapted from both:

    PCI: Avoid pci_dev_lock() AB/BA deadlock with sriov_numvfs_store()
    
    The sysfs sriov_numvfs_store() path acquires the device lock before the
    config space access lock:
    
      sriov_numvfs_store
        device_lock                 # A (1) acquire device lock
        sriov_configure
          vfio_pci_sriov_configure  # (for example)
            vfio_pci_core_sriov_configure
              pci_disable_sriov
                sriov_disable
                  pci_cfg_access_lock
                    pci_wait_cfg    # B (4) wait for dev->block_cfg_access == 0
    
    Previously, pci_dev_lock() acquired the config space access lock before the
    device lock:
    
      pci_dev_lock
        pci_cfg_access_lock
          dev->block_cfg_access = 1 # B (2) set dev->block_cfg_access = 1
        device_lock                 # A (3) wait for device lock
    
    Any path that uses pci_dev_lock(), e.g., pci_reset_function(), may
    deadlock with sriov_numvfs_store() if the operations occur in the sequence
    (1) (2) (3) (4).
    
    Avoid the deadlock by reversing the order in pci_dev_lock() so it acquires
    the device lock before the config space access lock, the same as the
    sriov_numvfs_store() path.
    
    [bhelgaas: combined and adapted commit log from Jay Zhou's independent
    subsequent posting:
    https://lore.kernel.org/r/20220404062539.1710-1-jianjay.zhou@xxxxxxxxxx]
    Link: https://lore.kernel.org/linux-pci/1583489997-17156-1-git-send-email-yangyicong@xxxxxxxxxxxxx/
    Also-posted-by: Jay Zhou <jianjay.zhou@xxxxxxxxxx>
    Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
    Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

> ---
>  drivers/pci/pci.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 9ecce435fb3f..61a6db1d21f6 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5103,19 +5103,19 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
>  
>  void pci_dev_lock(struct pci_dev *dev)
>  {
> -	pci_cfg_access_lock(dev);
>  	/* block PM suspend, driver probe, etc. */
>  	device_lock(&dev->dev);
> +	pci_cfg_access_lock(dev);
>  }
>  EXPORT_SYMBOL_GPL(pci_dev_lock);
>  
>  /* Return 1 on successful lock, 0 on contention */
>  int pci_dev_trylock(struct pci_dev *dev)
>  {
> -	if (pci_cfg_access_trylock(dev)) {
> -		if (device_trylock(&dev->dev))
> +	if (device_trylock(&dev->dev)) {
> +		if (pci_cfg_access_trylock(dev))
>  			return 1;
> -		pci_cfg_access_unlock(dev);
> +		device_unlock(&dev->dev);
>  	}
>  
>  	return 0;
> @@ -5124,8 +5124,8 @@ EXPORT_SYMBOL_GPL(pci_dev_trylock);
>  
>  void pci_dev_unlock(struct pci_dev *dev)
>  {
> -	device_unlock(&dev->dev);
>  	pci_cfg_access_unlock(dev);
> +	device_unlock(&dev->dev);
>  }
>  EXPORT_SYMBOL_GPL(pci_dev_unlock);
>  
> -- 
> 2.27.0
>