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

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Date:   Thu, 17 Nov 2022 16:07:48 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
CC:     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: Re: [PATCH V2] PCI/DOE: Detect on stack work items automatically

On Thu, Nov 17, 2022 at 04:05:24PM -0800, Ira wrote:
> From: Ira Weiny <ira.weiny@...el.com>

Sorry about the extra pre-patches listed below.  They are not needed.

> 
> 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

This is correct.

> prerequisite-patch-id: dfea657e07f37aa9d7c3d477d68b07f64fe78721
> prerequisite-patch-id: e27264e76e637214ee50cdab0e5854b223d44b4e

These are not needed...

Sorry, should I resend?

Ira

> -- 
> 2.37.2
>