From d12544fb2aa9944b180c35914031a8384ab082c1 Mon Sep 17 00:00:00 2001

From: Xiang Chen <chenxiang66@hisilicon.com>

Date: Tue, 22 Sep 2020 21:11:06 +0800

Subject: [PATCH] PM: runtime: Remove link state checks in

 rpm_get/put_supplier()

Git-commit: d12544fb2aa9944b180c35914031a8384ab082c1

References: git-fixes

Patch-mainline: v5.10-rc1

To support runtime PM for hisi SAS driver (the driver is in directory

drivers/scsi/hisi_sas), we add device link between scsi_device->sdev_gendev

(consumer device) and hisi_hba->dev(supplier device) with flags

DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE.

After runtime suspended consumers and supplier, unload the dirver which

causes a hung.

We found that it called function device_release_driver_internal() to

release the supplier device (hisi_hba->dev), as the device link was

busy, it set the device link state to DL_STATE_SUPPLIER_UNBIND, and

then it called device_release_driver_internal() to release the consumer

device (scsi_device->sdev_gendev).

Then it would try to call pm_runtime_get_sync() to resume the consumer

device, but because consumer-supplier relation existed, it would try

to resume the supplier first, but as the link state was already

DL_STATE_SUPPLIER_UNBIND, so it skipped resuming the supplier and only

resumed the consumer which hanged (it sends IOs to resume scsi_device

while the SAS controller is suspended).

Simple flow is as follows:

device_release_driver_internal -> (supplier device)

    if device_links_busy ->

	device_links_unbind_consumers ->

	    ...

	    WRITE_ONCE(link->status, DL_STATE_SUPPLIER_UNBIND)

	    device_release_driver_internal (consumer device)

    pm_runtime_get_sync -> (consumer device)

	...

	__rpm_callback ->

	    rpm_get_suppliers ->

		if link->state == DL_STATE_SUPPLIER_UNBIND -> skip the action of resuming the supplier

		...

    pm_runtime_clean_up_links

    ...

Correct suspend/resume ordering between a supplier device and its consumer

devices (resume the supplier device before resuming consumer devices, and

suspend consumer devices before suspending the supplier device) should be

guaranteed by runtime PM, but the state checks in rpm_get_supplier() and

rpm_put_supplier() break this rule, so remove them.

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>

[ rjw: Subject and changelog edits ]

Cc: All applicable <stable@vger.kernel.org>

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: Oliver Neukum <oneukum@suse.com>

---

 drivers/base/power/runtime.c |    3 +--

 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/base/power/runtime.c

+++ b/drivers/base/power/runtime.c

@@ -291,8 +291,7 @@ static int rpm_get_suppliers(struct devi

 				device_links_read_lock_held()) {

 		int retval;

-		if (!(link->flags & DL_FLAG_PM_RUNTIME) ||

-		    READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND)

+		if (!(link->flags & DL_FLAG_PM_RUNTIME))

 			continue;

 		retval = pm_runtime_get_sync(link->supplier);