Re: [PATCH] PCI: Fix AB-BA deadlock between aer_isr() and device_shutdown()

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jan 09, 2026 at 05:56:03PM +0800, Ziming Du wrote:
> During system shutdown, a deadlock may occur between AER recovery process
> and device shutdown as follows:
> 
> The device_shutdown path holds the device_lock throughout the entire
> process and waits for the irq handlers to complete when release nodes:
> 
>   device_shutdown
>     device_lock                      # A hold device_lock
>     pci_device_shutdown
>       pcie_port_device_remove
>         remove_iter
>           device_unregister
>             device_del
>               bus_remove_device
>                 device_release_driver
>                   devres_release_all
>                     release_nodes    # B wait for irq handlers

Can you add the wait location to these example?  release_nodes()
doesn't wait itself, so I guess it must be in a dr->node.release()
function?

And I guess it must be related to something in the IRQ path that is
held while aer_isr() runs?

> The aer_isr path will acquire device_lock in pci_bus_reset():
> 
>   aer_isr                            # B execute irq process
>     aer_isr_one_error
>       aer_process_err_devices
>         handle_error_source
>           pcie_do_recovery
>           aer_root_reset
>             pci_bus_error_reset
>               pci_bus_reset          # A acquire device_lock
> 
> The circular dependency causes system hang. Fix it by using
> pci_bus_trylock() instead of pci_bus_lock() in pci_bus_reset(). When the
> lock is unavailable, return -EAGAIN, as in similar cases.

pci_bus_error_reset() may use either pci_slot_reset() or
pci_bus_reset(), and this patch addresses only pci_bus_reset().  Is
the same deadlock possible in the pci_slot_reset() path?

> Fixes: c4eed62a2143 ("PCI/ERR: Use slot reset if available")
> Signed-off-by: Ziming Du <duziming2@huawei.com>
> ---
>  drivers/pci/pci.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 13dbb405dc31..7471bfa6f32e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5515,15 +5515,22 @@ static int pci_bus_reset(struct pci_bus *bus, bool probe)
>  	if (probe)
>  		return 0;
>  
> -	pci_bus_lock(bus);
> +	/*
> +	 * Replace blocking lock with trylock to prevent deadlock during bus reset.
> +	 * Same as above except return -EAGAIN if the bus cannot be locked.

Wrap this to fit in 80 columns like the rest of the file.

> +	 */
> +	if (pci_bus_trylock(bus)) {
>  
> -	might_sleep();
> +		might_sleep();
>  
> -	ret = pci_bridge_secondary_bus_reset(bus->self);
> +		ret = pci_bridge_secondary_bus_reset(bus->self);
>  
> -	pci_bus_unlock(bus);
> +		pci_bus_unlock(bus);
>  
> -	return ret;
> +		return ret;
> +	}
> +
> +	return -EAGAIN;
>  }
>  
>  /**
> -- 
> 2.43.0
>