In environments where free page reporting is disabled, a kernel panic is triggered when tearing down the virtio_balloon module:
[12261.808190] Call trace: [12261.808471] __list_del_entry_valid_or_report+0x18/0xe0 [12261.809064] vp_del_vqs+0x12c/0x270 [12261.809462] remove_common+0x80/0x98 [virtio_balloon] [12261.810034] virtballoon_remove+0xfc/0x158 [virtio_balloon] [12261.810663] virtio_dev_remove+0x68/0xf8 [12261.811108] device_release_driver_internal+0x17c/0x278 [12261.811701] driver_detach+0xd4/0x138 [12261.812117] bus_remove_driver+0x90/0xd0 [12261.812562] driver_unregister+0x40/0x70 [12261.813006] unregister_virtio_driver+0x20/0x38 [12261.813518] cleanup_module+0x20/0x7a8 [virtio_balloon] [12261.814109] __arm64_sys_delete_module+0x278/0x3d0 [12261.814654] invoke_syscall+0x5c/0x120 [12261.815086] el0_svc_common+0x90/0xf8 [12261.815506] do_el0_svc+0x2c/0x48 [12261.815883] el0_svc+0x3c/0xa8 [12261.816235] el0t_64_sync_handler+0x8c/0x108 [12261.816724] el0t_64_sync+0x198/0x1a0 The issue originates in vp_find_vqs_intx(). It kzalloc_objs() based on the nvqs count provided by the caller, virtio_balloon::init_vqs(). However, it is not always the case that all nvqs number of virtio_pci_vq_info objects will be properly populated. For example, when VIRTIO_BALLOON_F_FREE_PAGE_HINT is absent, the VIRTIO_BALLOON_VQ_FREE_PAGE-th item in the vp_dev->vqs array is actually never populated, and is still a zeroe-initialized virtio_pci_vq_info object, which is eventually going to trigger a __list_del_entry_valid_or_report() crash. Tested by applying this patch to a guest VM kernel with the VIRTIO_BALLOON_F_REPORTING feature enabled and the VIRTIO_BALLOON_F_FREE_PAGE_HINT feature disabled. Without this patch, unloading the virtio_balloon module triggers a panic. With this patch, no panic is observed. The fix is to use queue_idx to handle the case that vp_find_vqs_intx() skips vp_setup_vq() when caller provided null vqs_info[i].name, when the caller doesn't populate all nvqs number of virtqueue_info objects. Invariantly queue_idx is the correct index to store a successfully created and populated virtio_pci_vq_info object. As a result, now a virtio_pci_device object only stores queue_idx number of valid virtio_pci_vq_info objects in its vqs array when the for-loop over nvqs finishes (of course, without goto out_del_vqs). vp_find_vqs_msix() has similar issue, so fix it in the same way. This patch is marked as RFC because we are uncertain if any virtio-pci code implicitly requires virtio_pci_device's vqs array to always contain nvqs number of virtio_pci_vq_info objects, and to store zero-initialized virtio_pci_vq_info objects. We have not observed any issues in our testing, but insights or alternatives are welcome! Signed-off-by: Link Lin <[email protected]> Co-developed-by: Jiaqi Yan <[email protected]> Signed-off-by: Jiaqi Yan <[email protected]> --- drivers/virtio/virtio_pci_common.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c index da97b6a988de..9b32301529e5 100644 --- a/drivers/virtio/virtio_pci_common.c +++ b/drivers/virtio/virtio_pci_common.c @@ -423,14 +423,15 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs, vqs[i] = NULL; continue; } - vqs[i] = vp_find_one_vq_msix(vdev, queue_idx++, vqi->callback, + vqs[i] = vp_find_one_vq_msix(vdev, queue_idx, vqi->callback, vqi->name, vqi->ctx, false, &allocated_vectors, vector_policy, - &vp_dev->vqs[i]); + &vp_dev->vqs[queue_idx]); if (IS_ERR(vqs[i])) { err = PTR_ERR(vqs[i]); goto error_find; } + ++queue_idx; } if (!avq_num) @@ -485,13 +486,14 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned int nvqs, vqs[i] = NULL; continue; } - vqs[i] = vp_setup_vq(vdev, queue_idx++, vqi->callback, + vqs[i] = vp_setup_vq(vdev, queue_idx, vqi->callback, vqi->name, vqi->ctx, - VIRTIO_MSI_NO_VECTOR, &vp_dev->vqs[i]); + VIRTIO_MSI_NO_VECTOR, &vp_dev->vqs[queue_idx]); if (IS_ERR(vqs[i])) { err = PTR_ERR(vqs[i]); goto out_del_vqs; } + ++queue_idx; } if (!avq_num) -- 2.53.0.1213.gd9a14994de-goog
