Re: [PATCH] virtio-scsi: Skip setting affinity on uninitialized vq

[Paolo Bonzini]

Il 11/04/2014 03:23, Fam Zheng ha scritto:
> virtscsi_init calls virtscsi_remove_vqs on err, even before initializing
> the vqs. The latter calls virtscsi_set_affinity, so let's check the
> pointer there before setting affinity on it.
>
> This fixes a panic when setting device's num_queues=2 on RHEL 6.5:
>
> qemu-system-x86_64 ... \
> -device virtio-scsi-pci,id=scsi0,addr=0x13,...,num_queues=2 \
> -drive file=/stor/vm/dummy.raw,id=drive-scsi-disk,... \
> -device scsi-hd,drive=drive-scsi-disk,...
>
> [    0.354734] scsi0 : Virtio SCSI HBA
> [    0.379504] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
> [    0.380141] IP: [<ffffffff814741ef>] __virtscsi_set_affinity+0x4f/0x120
> [    0.380141] PGD 0
> [    0.380141] Oops: 0000 [#1] SMP
> [    0.380141] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.14.0+ #5
> [    0.380141] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007
> [    0.380141] task: ffff88003c9f0000 ti: ffff88003c9f8000 task.ti: ffff88003c9f8000
> [    0.380141] RIP: 0010:[<ffffffff814741ef>]  [<ffffffff814741ef>] __virtscsi_set_affinity+0x4f/0x120
> [    0.380141] RSP: 0000:ffff88003c9f9c08  EFLAGS: 00010256
> [    0.380141] RAX: 0000000000000000 RBX: ffff88003c3a9d40 RCX: 0000000000001070
> [    0.380141] RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000000
> [    0.380141] RBP: ffff88003c9f9c28 R08: 00000000000136c0 R09: ffff88003c801c00
> [    0.380141] R10: ffffffff81475229 R11: 0000000000000008 R12: 0000000000000000
> [    0.380141] R13: ffffffff81cc7ca8 R14: ffff88003cac3d40 R15: ffff88003cac37a0
> [    0.380141] FS:  0000000000000000(0000) GS:ffff88003e400000(0000) knlGS:0000000000000000
> [    0.380141] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [    0.380141] CR2: 0000000000000020 CR3: 0000000001c0e000 CR4: 00000000000006f0
> [    0.380141] Stack:
> [    0.380141]  ffff88003c3a9d40 0000000000000000 ffff88003cac3d80 ffff88003cac3d40
> [    0.380141]  ffff88003c9f9c48 ffffffff814742e8 ffff88003c26d000 ffff88003c26d000
> [    0.380141]  ffff88003c9f9c68 ffffffff81474321 ffff88003c26d000 ffff88003c3a9d40
> [    0.380141] Call Trace:
> [    0.380141]  [<ffffffff814742e8>] virtscsi_set_affinity+0x28/0x40
> [    0.380141]  [<ffffffff81474321>] virtscsi_remove_vqs+0x21/0x50
> [    0.380141]  [<ffffffff81475231>] virtscsi_init+0x91/0x240
> [    0.380141]  [<ffffffff81365290>] ? vp_get+0x50/0x70
> [    0.380141]  [<ffffffff81475544>] virtscsi_probe+0xf4/0x280
> [    0.380141]  [<ffffffff81363ea5>] virtio_dev_probe+0xe5/0x140
> [    0.380141]  [<ffffffff8144c669>] driver_probe_device+0x89/0x230
> [    0.380141]  [<ffffffff8144c8ab>] __driver_attach+0x9b/0xa0
> [    0.380141]  [<ffffffff8144c810>] ? driver_probe_device+0x230/0x230
> [    0.380141]  [<ffffffff8144c810>] ? driver_probe_device+0x230/0x230
> [    0.380141]  [<ffffffff8144ac1c>] bus_for_each_dev+0x8c/0xb0
> [    0.380141]  [<ffffffff8144c499>] driver_attach+0x19/0x20
> [    0.380141]  [<ffffffff8144bf28>] bus_add_driver+0x198/0x220
> [    0.380141]  [<ffffffff8144ce9f>] driver_register+0x5f/0xf0
> [    0.380141]  [<ffffffff81d27c91>] ? spi_transport_init+0x79/0x79
> [    0.380141]  [<ffffffff8136403b>] register_virtio_driver+0x1b/0x30
> [    0.380141]  [<ffffffff81d27d19>] init+0x88/0xd6
> [    0.380141]  [<ffffffff81d27c18>] ? scsi_init_procfs+0x5b/0x5b
> [    0.380141]  [<ffffffff81ce88a7>] do_one_initcall+0x7f/0x10a
> [    0.380141]  [<ffffffff81ce8aa7>] kernel_init_freeable+0x14a/0x1de
> [    0.380141]  [<ffffffff81ce8b3b>] ? kernel_init_freeable+0x1de/0x1de
> [    0.380141]  [<ffffffff817dec20>] ? rest_init+0x80/0x80
> [    0.380141]  [<ffffffff817dec29>] kernel_init+0x9/0xf0
> [    0.380141]  [<ffffffff817e68fc>] ret_from_fork+0x7c/0xb0
> [    0.380141]  [<ffffffff817dec20>] ? rest_init+0x80/0x80
> [    0.380141] RIP  [<ffffffff814741ef>] __virtscsi_set_affinity+0x4f/0x120
> [    0.380141]  RSP <ffff88003c9f9c08>
> [    0.380141] CR2: 0000000000000020
> [    0.380141] ---[ end trace 8074b70c3d5e1d73 ]---
> [    0.475018] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
> [    0.475018]
> [    0.475068] Kernel Offset: 0x0 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffff9fffffff)
> [    0.475068] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
>
> Signed-off-by: Fam Zheng <famz@xxxxxxxxxx>
> ---
>  drivers/scsi/virtio_scsi.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index 16bfd50..3019267 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -750,8 +750,12 @@ static void __virtscsi_set_affinity(struct virtio_scsi *vscsi, bool affinity)
>
>  		vscsi->affinity_hint_set = true;
>  	} else {
> -		for (i = 0; i < vscsi->num_queues; i++)
> +		for (i = 0; i < vscsi->num_queues; i++) {
> +			if (!vscsi->req_vqs[i].vq) {
> +				continue;
> +			}
>  			virtqueue_set_affinity(vscsi->req_vqs[i].vq, -1);
> +		}
>
>  		vscsi->affinity_hint_set = false;
>  	}

You put the if inside the loop, but it's really all or nothing since the 
failure point is find_vqs.

Not a problem though; the queues are few and this is not a hot path anyway.

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Paolo
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