From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.233 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793276230; b=jDIQE0WItcp6Os6vgegtBmvKu4SE41QhyeeSXp0R/RoatVqqhyie1UkOcv9x+RPuEK3T CODl7200DPhYK3jwIj8can5viT6xMHyaA07b+hJGNQ88cdf7Td/YuctFQIET9VssdFotC CntCVj0c4aODKYbkl7ZQ0CvIaFPI9GowuxLzNtaj8vf/g/6+rYR+c2UT+8WLBQyBfiRas k7O4CE8DbBYKq3rNY95VLGT32EVFS+zJQeXNj0+xi9lQlP3UvZzgBpHxLMoQni6uNV5Q1 Furb3/dbvI4RGtkqGgDMuB6YTCjMreLwHhrE81g/4M5+vW/jnuZnzyImRHYHDC+Ke7Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793276230; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:MIME-Version:Content-Transfer-Encoding; bh=o1J44ApCZcXZ8+H5KZ4BMdIIPj/zA2Frewpp0GrFExY=; b=WFjWrxMXwYtXHVvZohtJa28WqXh468DoX6Il6qsomm6LwkwLcM+9tTf7eRImy16yy5qW J5TR+gH9itqHmf1DaGUPhIpPdV3DBhxE0BRth2J7egC+56vaYxTtIxqY01dEHdufICSSB RNJD+5TodOZFMFaoFMglW91DRxbhylRChoA6zXeBmCBE6XEMO/zD8Gd+igNuOWuT4Cn3r LdqhDg1H1zPJTjlHH9L8p5anep/0WP1PjweXZ4cMUJMaJ5IO/la/Py1xKTD2VJHAMrdPs pXsAu4aFOiMNlYJEeZXJCIrIc6y0tiTQK6H+7s97xyqYzv00ATtr4eQceROpirlk34w== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=geHG0mKk; arc=none smtp.remote-ip=95.215.58.233 Received: from mta1.migadu.com (out-233.mta1.migadu.com [95.215.58.233]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2F41E606A31A for ; Thu, 29 Oct 2026 12:17:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 2F41E606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=geHG0mKk X-Envelope-To: virtualization@lists.linux.dev DKIM-Signature: a=rsa-sha256; bh=xrtJCHs8Ijzc5X00K4uBgaCna2u4+yB/U6fjq8IJbpA=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793276221; v=1; x=1793881021; b=geHG0mKk9WveXv3S/h6GdbvynywlHP48tiIATPe10rrNqbyRzAMdqqKYdbSv/D/wkzK/OzV2 giEOcwNgIsGtOwUISONMKSTov/76ATvfpbyBq2LIfRepHHkjDI03D9ER5Sr9huR/DEflzAHhelY QOfoNCW/6NR69PJ26fkS371o= X-Envelope-To: virtualization@lists.linux.dev Received: by smtp.migadu.com with ESMTPS id 2f4d8c56ac62a9a2; Thu, 29 Oct 2026 12:17:01 +0000 X-Mizu-Trace-ID: 2f4d8c56ac62a9a2 X-Migadu-Flow: FLOW_OUT From: Zenghui Yu To: virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Cc: mst@redhat.com, jasowangio@gmail.com, eperezma@redhat.com, xuanzhuo@linux.alibaba.com, nicolinc@nvidia.com, jgg@nvidia.com, "Zenghui Yu (Huawei)" Subject: [PATCH v2] virtio_pci: don't take the MSI mutex under cpu_hotplug_lock Date: Thu, 29 Oct 2026 20:16:48 +0800 Message-ID: <20261029121648.22155-1-zenghui.yu@linux.dev> X-Mailer: git-send-email 2.56.0 X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Zenghui Yu (Huawei)" Lockdep reports the following circular locking dependency when a virtio-net device is probed with lockdep enabled on a system whose devices sit behind an IOMMU: ====================================================== WARNING: possible circular locking dependency detected 7.3.0-rc1+ #84 Not tainted ------------------------------------------------------ kworker/u34:0/57 is trying to acquire lock: ffff800104f83ee8 (&md->mutex){+.+.}-{4:4}, at: msi_domain_get_virq+0xf0/0x118 but task is already holding lock: ffffc00081edd930 (cpu_hotplug_lock){++++}-{0:0}, at: cpus_read_lock+0x10/0x1c which lock already depends on the new lock. Chain exists of: &md->mutex --> &group->mutex --> cpu_hotplug_lock The cycle is composed of three dependencies: * cpu_hotplug_lock -> &md->mutex (which triggers the splat). virtio_net's init_vqs() calls cpus_read_lock() around virtnet_set_affinity(), which reaches vp_set_vq_affinity(). That calls pci_irq_vector(), which takes the per-device MSI mutex (&dev->msi.data->mutex) via msi_domain_get_virq(). * &md->mutex -> &domain->mutex -> &group->mutex. MSI-X allocation of any device behind the IOMMU holds the MSI mutex while allocating interrupts through the IRQ domain hierarchy. The MSI parent domain (GICv2m, or ITS likewise) calls iommu_dma_prepare_msi() from its .alloc() to map the MSI doorbell, which takes the IOMMU group mutex. * &group->mutex -> cpu_hotplug_lock. bus_iommu_probe() calls iommu_setup_dma_ops() under the group mutex; initializing the IOVA rcaches registers a cpuhp instance, which takes cpu_hotplug_lock. The cycle only became complete since commit 288683c92b1a ("iommu: Make iommu_dma_prepare_msi() into a generic operation"), where iommu_dma_prepare_msi() switched to use the group mutex. pci_irq_vector() is a pure lookup of a vector that is bound to the queue for the whole lifetime of the queue, so there is no reason to take the MSI mutex for it from cpu hotplug locked contexts. Cache the IRQ number in virtio_pci_vq_info {} at vector binding time and make vp_set_vq_affinity() use the cached value. This also covers the CPU hotplug callbacks (virtnet_cpu_online/virtnet_cpu_dead), which call virtnet_set_affinity() with cpu_hotplug_lock already held. Signed-off-by: Zenghui Yu (Huawei) --- * From v1 [1]: - drop the comment in vp_setup_vq() (Michael S. Tsirkin) - use "if/else" instead of pre-initializing virq to 0 (Michael S. Tsirkin) [1] https://lore.kernel.org/20261029084043.19409-1-zenghui.yu@linux.dev drivers/virtio/virtio_pci_common.c | 8 +++++++- drivers/virtio/virtio_pci_common.h | 3 +++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c index b90c174450b2..21a4b1f97c61 100644 --- a/drivers/virtio/virtio_pci_common.c +++ b/drivers/virtio/virtio_pci_common.c @@ -224,6 +224,12 @@ static struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned int in goto out_info; info->vq = vq; + + if (msix_vec != VIRTIO_MSI_NO_VECTOR) + info->virq = pci_irq_vector(vp_dev->pci_dev, msix_vec); + else + info->virq = 0; + if (callback) { spin_lock_irqsave(&vp_dev->lock, flags); if (!vp_is_slow_path_vector(msix_vec)) @@ -571,7 +577,7 @@ int vp_set_vq_affinity(struct virtqueue *vq, const struct cpumask *cpu_mask) if (vp_dev->msix_enabled) { mask = vp_dev->msix_affinity_masks[info->msix_vector]; - irq = pci_irq_vector(vp_dev->pci_dev, info->msix_vector); + irq = info->virq; if (!cpu_mask) irq_update_affinity_hint(irq, NULL); else { diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h index 8cd01de27baf..18b15a5f84ae 100644 --- a/drivers/virtio/virtio_pci_common.h +++ b/drivers/virtio/virtio_pci_common.h @@ -40,6 +40,9 @@ struct virtio_pci_vq_info { /* MSI-X vector (or none) */ unsigned int msix_vector; + + /* Linux IRQ number of msix_vector, or 0 if not mapped */ + unsigned int virq; }; struct virtio_pci_admin_vq { -- 2.56.0