linux-kernel - Re: system hung up when offlining CPUs

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Message-ID: <20170821131809.GA17564@lst.de>
Date:   Mon, 21 Aug 2017 15:18:09 +0200
From:   Christoph Hellwig <hch@....de>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     YASUAKI ISHIMATSU <yasu.isimatu@...il.com>, tglx@...utronix.de,
        axboe@...nel.dk, mpe@...erman.id.au, keith.busch@...el.com,
        peterz@...radead.org, LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: system hung up when offlining CPUs

Can you try the patch below please?

---
>From d5f59cb7a629de8439b318e1384660e6b56e7dd8 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@....de>
Date: Mon, 21 Aug 2017 14:24:11 +0200
Subject: virtio_pci: fix cpu affinity support

Commit 0b0f9dc5 ("Revert "virtio_pci: use shared interrupts for
virtqueues"") removed the adjustment of the pre_vectors for the virtio
MSI-X vector allocation which was added in commit fb5e31d9 ("virtio:
allow drivers to request IRQ affinity when creating VQs"). This will
lead to an incorrect assignment of MSI-X vectors, and potential
deadlocks when offlining cpus.

Signed-off-by: Christoph Hellwig <hch@....de>
Fixes: 0b0f9dc5 ("Revert "virtio_pci: use shared interrupts for virtqueues")
Reported-by: YASUAKI ISHIMATSU <yasu.isimatu@...il.com>
---
 drivers/virtio/virtio_pci_common.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 007a4f366086..1c4797e53f68 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -107,6 +107,7 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
 {
 	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 	const char *name = dev_name(&vp_dev->vdev.dev);
+	unsigned flags = PCI_IRQ_MSIX;
 	unsigned i, v;
 	int err = -ENOMEM;
 
@@ -126,10 +127,13 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
 					GFP_KERNEL))
 			goto error;
 
+	if (desc) {
+		flags |= PCI_IRQ_AFFINITY;
+		desc->pre_vectors++; /* virtio config vector */
+	}
+
 	err = pci_alloc_irq_vectors_affinity(vp_dev->pci_dev, nvectors,
-					     nvectors, PCI_IRQ_MSIX |
-					     (desc ? PCI_IRQ_AFFINITY : 0),
-					     desc);
+					     nvectors, flags, desc);
 	if (err < 0)
 		goto error;
 	vp_dev->msix_enabled = 1;
-- 
2.11.0