PCI/DOE: Silence WARN splat with CONFIG_DEBUG_OBJECTS=y

Gregory Price reports a WARN splat with CONFIG_DEBUG_OBJECTS=y upon CXL
probing because pci_doe_submit_task() invokes INIT_WORK() instead of
INIT_WORK_ONSTACK() for a work_struct that was allocated on the stack.

All callers of pci_doe_submit_task() allocate the work_struct on the
stack, so replace INIT_WORK() with INIT_WORK_ONSTACK() as a backportable
short-term fix.

The long-term fix implemented by a subsequent commit is to move to a
synchronous API which allocates the work_struct internally in the DOE
library.

Stacktrace for posterity:

WARNING: CPU: 0 PID: 23 at lib/debugobjects.c:545 __debug_object_init.cold+0x18/0x183
CPU: 0 PID: 23 Comm: kworker/u2:1 Not tainted 6.1.0-0.rc1.20221019gitaae703b02f92.17.fc38.x86_64 #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Call Trace:
 pci_doe_submit_task+0x5d/0xd0
 pci_doe_discovery+0xb4/0x100
 pcim_doe_create_mb+0x219/0x290
 cxl_pci_probe+0x192/0x430
 local_pci_probe+0x41/0x80
 pci_device_probe+0xb3/0x220
 really_probe+0xde/0x380
 __driver_probe_device+0x78/0x170
 driver_probe_device+0x1f/0x90
 __driver_attach_async_helper+0x5c/0xe0
 async_run_entry_fn+0x30/0x130
 process_one_work+0x294/0x5b0

Fixes: 9d24322 ("PCI/DOE: Add DOE mailbox support functions")
Link: https://lore.kernel.org/linux-cxl/Y1bOniJliOFszvIK@memverge.com/
Reported-by: Gregory Price <gregory.price@memverge.com>
Tested-by: Ira Weiny <ira.weiny@intel.com>
Tested-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Gregory Price <gregory.price@memverge.com>
Cc: stable@vger.kernel.org # v6.0+
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/67a9117f463ecdb38a2dbca6a20391ce2f1e7a06.1678543498.git.lukas@wunner.de
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/pci/doe.c

@@ -523,6 +523,8 @@ EXPORT_SYMBOL_GPL(pci_doe_supports_prot);
  * task->complete will be called when the state machine is done processing this
  * task.
  *
+ * @task must be allocated on the stack.
+ *
  * Excess data will be discarded.
  *
  * RETURNS: 0 when task has been successfully queued, -ERRNO on error
@@ -544,7 +546,7 @@ int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
 		return -EIO;
 
 	task->doe_mb = doe_mb;
-	INIT_WORK(&task->work, doe_statemachine_work);
+	INIT_WORK_ONSTACK(&task->work, doe_statemachine_work);
 	queue_work(doe_mb->work_queue, &task->work);
 	return 0;
 }