linux-kernel - [PATCH V2] PCI/DOE: Detect on stack work items automatically

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Date:   Thu, 17 Nov 2022 16:05:24 -0800
From:   ira.weiny@...el.com
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Gregory Price <gregory.price@...verge.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Lukas Wunner <lukas@...ner.de>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-cxl@...r.kernel.org
Subject: [PATCH V2] PCI/DOE: Detect on stack work items automatically

From: Ira Weiny <ira.weiny@...el.com>

Work item initialization needs to be done with either
INIT_WORK_ONSTACK() or INIT_WORK() depending on how the work item is
allocated.

The callers of pci_doe_submit_task() allocate struct pci_doe_task on the
stack and pci_doe_submit_task() incorrectly used INIT_WORK().

Jonathan suggested creating doe task allocation macros such as
DECLARE_CDAT_DOE_TASK_ONSTACK().[1]  The issue with this is the work
function is not known to the callers and must be initialized correctly.

A follow up suggestion was to have an internal 'pci_doe_work' item
allocated by pci_doe_submit_task().[2]  This requires an allocation which
could restrict the context where tasks are used.

Another idea was to have an intermediate step to initialize the task
struct with a new call.[3]  This added a lot of complexity.

Lukas pointed out that object_is_on_stack() is available to detect this
automatically.

Use object_is_on_stack() to determine the correct init work function to
call.

[1] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@huawei.com/T/#m88a7f50dcce52f30c8bf5c3dcc06fa9843b54a2d
[2] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@huawei.com/T/#m63c636c5135f304480370924f4d03c00357be667
[3] https://lore.kernel.org/all/20221115011943.1051039-1-ira.weiny@intel.com/

Cc: Bjorn Helgaas <helgaas@...nel.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Reported-by: Gregory Price <gregory.price@...verge.com>
Reported-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Suggested-by: Lukas Wunner <lukas@...ner.de>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>

---
Changes from V1
	Update oneliner
	Use object_is_on_stack() to make this a simple fix
---
 drivers/pci/doe.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
index e402f05068a5..42de517022d9 100644
--- a/drivers/pci/doe.c
+++ b/drivers/pci/doe.c
@@ -19,6 +19,7 @@
 #include <linux/pci.h>
 #include <linux/pci-doe.h>
 #include <linux/workqueue.h>
+#include <linux/sched/task_stack.h>
 
 #define PCI_DOE_PROTOCOL_DISCOVERY 0
 
@@ -529,7 +530,10 @@ 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);
+	if (object_is_on_stack(&task->work))
+		INIT_WORK_ONSTACK(&task->work, doe_statemachine_work);
+	else
+		INIT_WORK(&task->work, doe_statemachine_work);
 	queue_work(doe_mb->work_queue, &task->work);
 	return 0;
 }

base-commit: 30a0b95b1335e12efef89dd78518ed3e4a71a763
prerequisite-patch-id: dfea657e07f37aa9d7c3d477d68b07f64fe78721
prerequisite-patch-id: e27264e76e637214ee50cdab0e5854b223d44b4e
-- 
2.37.2