linux-kernel - Re: [PATCH v2] virtio_pci: avoid to request intx irq if pin is zero

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Date:   Wed, 28 Sep 2022 01:59:19 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Angus Chen <angus.chen@...uarmicro.com>
Cc:     jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] virtio_pci: avoid to request intx irq if pin is zero

Thanks! More minor issues to address

On Wed, Sep 28, 2022 at 01:35:22PM +0800, Angus Chen wrote:
> The background is that we use dpu in cloud computing,the arch is x86,80
> cores.We will have a lots of virtio devices,like 512 or more.
> When we probe about 200 virtio_blk devices,it will fail and
> the stack is print as follows:
> 
> [25338.485128] virtio-pci 0000:b3:00.0: virtio_pci: leaving for legacy driver
> [25338.496174] genirq: Flags mismatch irq 0. 00000080 (virtio418) vs. 00015a00 (timer)
> [25338.503822] CPU: 20 PID: 5431 Comm: kworker/20:0 Kdump: loaded Tainted: G           OE    --------- -  - 4.18.0-305.30.1.el8.x86_64
> [25338.516403] Hardware name: Inspur NF5280M5/YZMB-00882-10E, BIOS 4.1.21 08/25/2021
> [25338.523881] Workqueue: events work_for_cpu_fn
> [25338.528235] Call Trace:
> [25338.530687]  dump_stack+0x5c/0x80
> [25338.534000]  __setup_irq.cold.53+0x7c/0xd3
> [25338.538098]  request_threaded_irq+0xf5/0x160
> [25338.542371]  vp_find_vqs+0xc7/0x190
> [25338.545866]  init_vq+0x17c/0x2e0 [virtio_blk]
> [25338.550223]  ? ncpus_cmp_func+0x10/0x10
> [25338.554061]  virtblk_probe+0xe6/0x8a0 [virtio_blk]
> [25338.558846]  virtio_dev_probe+0x158/0x1f0
> [25338.562861]  really_probe+0x255/0x4a0
> [25338.566524]  ? __driver_attach_async_helper+0x90/0x90
> [25338.571567]  driver_probe_device+0x49/0xc0
> [25338.575660]  bus_for_each_drv+0x79/0xc0
> [25338.579499]  __device_attach+0xdc/0x160
> [25338.583337]  bus_probe_device+0x9d/0xb0
> [25338.587167]  device_add+0x418/0x780
> [25338.590654]  register_virtio_device+0x9e/0xe0
> [25338.595011]  virtio_pci_probe+0xb3/0x140
> [25338.598941]  local_pci_probe+0x41/0x90
> [25338.602689]  work_for_cpu_fn+0x16/0x20
> [25338.606443]  process_one_work+0x1a7/0x360
> [25338.610456]  ? create_worker+0x1a0/0x1a0
> [25338.614381]  worker_thread+0x1cf/0x390
> [25338.618132]  ? create_worker+0x1a0/0x1a0
> [25338.622051]  kthread+0x116/0x130
> [25338.625283]  ? kthread_flush_work_fn+0x10/0x10
> [25338.629731]  ret_from_fork+0x1f/0x40
> [25338.633395] virtio_blk: probe of virtio418 failed with error -16
> 
> The log :
> "genirq: Flags mismatch irq 0. 00000080 (virtio418) vs. 00015a00 (timer)"
> was print because of the irq 0 is used by timer exclusive,and when
> vp_find_vqs call vp_find_vqs_msix and return false twice for
> whatever reason,then it will call vp_find_vqs_intx for the last try.
> Because vp_dev->pci_dev->irq is zero,so it will be request irq 0 with
> flag IRQF_SHARED,we will get a backtrace like above.
> 
> according to PCI spec , Devices (or device functions)
> that do not use an interrupt pin must put a 0 in this register.

Pls add quotes and add "Interrupt Pin:" to make it clear in which register.

> So if vp_dev->pci_dev->pin is zero, maybe we should not request legacy
> interrupt.

and drop "maybe" here pls. I guess it sounds impolite to you but
as the patch author you get to make the tough decisions :)

> 
> Signed-off-by: Angus Chen <angus.chen@...uarmicro.com>
> Suggested-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> v2:
> - Decide whether to request an intx interrupt by pin instead of irq
> - suggested by mst
> 
> v1:https://lore.kernel.org/virtualization/20220928000228-mutt-send-email-mst@kernel.org/T/#u
> 
>  drivers/virtio/virtio_pci_common.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index ad258a9d3b9f..81225e503e69 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -362,6 +362,9 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned int nvqs,
>  	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>  	int i, err, queue_idx = 0;
>  
> +	if (vp_dev->pci_dev->pin == 0)
> +		return -EINVAL;
> +

Pls use !pin for brevity.

>  	vp_dev->vqs = kcalloc(nvqs, sizeof(*vp_dev->vqs), GFP_KERNEL);
>  	if (!vp_dev->vqs)
>  		return -ENOMEM;


So, this is mostly ok. The only issue is this:


int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
                struct virtqueue *vqs[], vq_callback_t *callbacks[],
                const char * const names[], const bool *ctx,
                struct irq_affinity *desc)
{
        int err;

        /* Try MSI-X with one vector per queue. */
        err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, true, ctx, desc);
        if (!err)
                return 0;
        /* Fallback: MSI-X with one vector for config, one shared for queues. */
        err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, false, ctx, desc);
        if (!err)
                return 0;
        /* Finally fall back to regular interrupts. */
        return vp_find_vqs_intx(vdev, nvqs, vqs, callbacks, names, ctx);
}


So the real source of failure to use msix, will be overwritten in err by EINVAL.

How about moving the "if" to vp_find_vqs?
E.g.
	/* Is there an interrupt pin? If not give up. */
	if (!vdev->pci_dev->pin)
		return err;


> -- 
> 2.17.1