linux-kernel - Calling queue_work() multiple times with the same work

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Date:   Thu, 20 May 2021 08:39:56 -0400
From:   Jason Andryuk <jandryuk@...il.com>
To:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Calling queue_work() multiple times with the same work_struct

Hi,

I'm looking for clarification of the behavior of queue_work().  From
the header description, I'm not sure if I need additional complexity
for re-queuing work.

I want to ensure the following cases all occur when calling queue_work().
1) work_struct not queued -> work_struct queued
2) work_struct queued -> work_struct queued (no change)
3) work_struct running -> work_struct queued (so it will run again)

1 & 2 look supported from workqueue.h.  Is the 3rd case true and
guaranteed?  Is it okay to re-use the same work_struct in that case
while it's being executed?  A work_struct function can re-queue
itself, so I hope #3 is supported.

The virtual device I'm working on has a single interrupt shared for
multiple rings.  So whenever an interrupt occurs, I need to re-queue
the single work_struct on the workqueue to ensure we don't miss an
event.  That is, we need to re-iterate all the rings if the interrupt
comes halfway through processing the list of rings.  If multiple
interrupts come through while running, we only need to re-queue a
single work item for all of them.

Below is what I hope works for the code to give something tangible.

Thank you,
Jason

DECLARE_WORK(argo_work, argo_work_fn);
static struct workqueue_struct *argo_wq = alloc_workqueue("argo_wq",
                    WQ_UNBOUND | WQ_HIGHPRI | WQ_CPU_INTENSIVE | WQ_SYSFS, 1);

static void argo_work_fn(struct work_struct *work)
{
    argo_interrupt_rx();  /* iterates multiple "rings" */
    argo_notify();
}

static irqreturn_t argo_interrupt(int irq, void *dev_id)
{
    queue_work(argo_wq, &argo_work);

    return IRQ_HANDLED;
}