linux-kernel - Re: [PATCH] PCI/doe: Fix work struct declaration

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Message-ID: <20221116100939.GA32050@wunner.de>
Date:   Wed, 16 Nov 2022 11:09:39 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Gregory Price <gregory.price@...verge.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>, linux-cxl@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI/doe: Fix work struct declaration

On Mon, Nov 14, 2022 at 05:19:43PM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> The callers of pci_doe_submit_task() allocate the pci_doe_task on the
> stack.  This causes the work structure to be allocated on the stack
> without pci_doe_submit_task() knowing.  Work item initialization needs
> to be done with either INIT_WORK_ONSTACK() or INIT_WORK() depending on
> how the work item is allocated.
> 
> 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.
> 
> Compromise with an intermediate step to initialize the task struct with
> a new call pci_doe_init_task() which must be called prior to submit
> task.
> 
> [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

We have object_is_on_stack(), included from <linux/sched/task_stack.h>.

So you could just autosense in pci_doe_submit_task() whether
pci_doe_task is on the stack and call the appropriate INIT_WORK
variant.

Any reason not to do that?

Thanks,

Lukas