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From:   Angus Chen <angus.chen@jaguarmicro.com>
To:     jasowang@redhat.com, mst@redhat.com
Cc:     virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org,
        Angus Chen <angus.chen@jaguarmicro.com>
Subject: [PATCH v2] virtio_pci: avoid to request intx irq if pin is zero
Date:   Wed, 28 Sep 2022 13:35:22 +0800
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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.
So if vp_dev->pci_dev->pin is zero, maybe we should not request legacy
interrupt.

Signed-off-by: Angus Chen <angus.chen@jaguarmicro.com>
Suggested-by: Michael S. Tsirkin <mst@redhat.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;
+
 	vp_dev->vqs = kcalloc(nvqs, sizeof(*vp_dev->vqs), GFP_KERNEL);
 	if (!vp_dev->vqs)
 		return -ENOMEM;
-- 
2.17.1