[PATCH 1/5] driver core: Support two-pass driver shutdown

[Jeremy Allison]

On Thu, Jan 04, 2024 at 03:12:11PM +0200, Sagi Grimberg wrote:
>
>
>On 1/3/24 23:04, Jeremy Allison wrote:
>>From: Tanjore Suresh <tansuresh at google.com>
>>
>>This changes the bus driver interface with an additional entry point
>>to enable devices to implement two-pass shutdown. The existing
>>synchronous interface to shutdown is called, and if a shutdown_wait
>>method is defined the device is moved to an alternate list.
>>
>>Once the shutdown method is called for all devices, the
>>shutdown_wait method is then called synchronously for
>>all devices on the alternate list.
>>
>>Signed-off-by: Tanjore Suresh <tansuresh at google.com>
>>Signed-off-by: Jeremy Allison <jallison at ciq.com>
>>---
>>  drivers/base/core.c        | 37 +++++++++++++++++++++++++++++++++++++
>>  include/linux/device/bus.h |  6 +++++-
>>  2 files changed, 42 insertions(+), 1 deletion(-)
>>
>>diff --git a/drivers/base/core.c b/drivers/base/core.c
>>index 67ba592afc77..e1f4c54de3e1 100644
>>--- a/drivers/base/core.c
>>+++ b/drivers/base/core.c
>>@@ -4725,6 +4725,7 @@ EXPORT_SYMBOL_GPL(device_change_owner);
>>  void device_shutdown(void)
>>  {
>>  	struct device *dev, *parent;
>>+	LIST_HEAD(shutdown_wait_list);
>>  	wait_for_device_probe();
>>  	device_block_probing();
>>@@ -4769,10 +4770,17 @@ void device_shutdown(void)
>>  				dev_info(dev, "shutdown_pre\n");
>>  			dev->class->shutdown_pre(dev);
>>  		}
>>+
>>  		if (dev->bus && dev->bus->shutdown) {
>>  			if (initcall_debug)
>>  				dev_info(dev, "shutdown\n");
>>  			dev->bus->shutdown(dev);
>>+			/*
>>+			 * Only put the device on the shutdown_wait_list
>>+			 * if a shutdown_wait() method is also defined.
>>+			 */
>>+			if (dev->bus->shutdown_wait)
>>+				list_add(&dev->kobj.entry, &shutdown_wait_list);
>>  		} else if (dev->driver && dev->driver->shutdown) {
>>  			if (initcall_debug)
>>  				dev_info(dev, "shutdown\n");
>>@@ -4789,6 +4797,35 @@ void device_shutdown(void)
>>  		spin_lock(&devices_kset->list_lock);
>>  	}
>>  	spin_unlock(&devices_kset->list_lock);
>>+
>>+	/*
>>+	 * Second pass only for devices that have configured
>>+	 * a shutdown_wait() method.
>>+	 */
>>+	while (!list_empty(&shutdown_wait_list)) {
>>+		dev = list_entry(shutdown_wait_list.next, struct device,
>>+				kobj.entry);
>>+		parent = get_device(dev->parent);
>>+		get_device(dev);
>>+		/*
>>+		 * Make sure the device is off the  list
>>+		 */
>>+		list_del_init(&dev->kobj.entry);
>>+		if (parent)
>>+			device_lock(parent);
>>+		device_lock(dev);
>>+		if (dev->bus && dev->bus->shutdown_wait) {
>
>How can dev->bus or dev->bus->shutdown_wait be null at this
>point?

It's a fair cop :-). That's just paranoia. I'll remove :-).