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Date: Wed, 28 Sep 2022 06:21:55 +0000
From: Angus Chen <angus.chen@...uarmicro.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: "jasowang@...hat.com" <jasowang@...hat.com>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] virtio_pci: avoid to request intx irq if pin is zero
> -----Original Message-----
> From: Michael S. Tsirkin <mst@...hat.com>
> Sent: Wednesday, September 28, 2022 1:59 PM
> 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.
Yes,that looks better.
>
> > 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;
>
OK. vp_find_vqs_intx is staic and it only be called by vp_find_vqs, and it will avoids a single press into the stack .
I will send this in another version.
>
> > --
> > 2.17.1
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