[SeaBIOS] Bug in SeaBIOS virtio-ring handling bug with vhost-scsi-pci

Nicholas A. Bellinger nab at linux-iscsi.org
Tue Apr 9 06:09:54 CEST 2013


Ping.

Any ideas on this one..?  It seems like this bug would be effecting
non vhost-scsi-pci code as well..

--nab

On Thu, 2013-04-04 at 19:59 -0700, Nicholas A. Bellinger wrote:
> Hi Paolo & Co,
> 
> So I've been running into another bug with SeaBIOS w/ virtio-scsi +
> vhost-scsi-pci code..
> 
> During the last weeks debugging on the QEMU vhost memory re-mapping bug,
> my seabios builds have been using a smaller target ID (16) for scanning
> than the default hard coded value of 256 in init_virtio_scsi().
> 
> After bumping this value back to 256 recently, a bogus out_num value
> from vhost_get_vq_desc() start appearing on the tcm_vhost side:
> 
> [17348.044031] Invalid buffer layout out: 0 in: 2
> 
> After adding more debug output to SeaBIOS, the vring->num value appears
> to be reset from the expected MAX_QUEUE_NUM=128, then incremented each
> time after vring_more_used() is called to poll for completion.. 
> 
> init virtio-scsi
> found virtio-scsi at 0:4
> vring_init Setting vr->num: 128
> Calling virtio_scsi_scan_target for target: 0
> Searching bootorder for: /pci at i0cf8/*@4/*@0/*@0,0
> virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2
> virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 128
> vring_add_buf, vr: 0x000ed404 vr->num: 128
> vring_add_buf, head: 0, index: 0
> vring_add_buf, setting desc[prev=2].flags
> vring_add_buf, setting free_head: 3
> vring_add_buf, setting q->vdata[head=0]
> vring_add_buf, setting q->ring[av=0]
> virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 128
> virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 128
> virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 1
>                                           ^^^^^^^^^^^^^^^^^^^^^^^^^   
> 
>    Reset from 128 to 1 immediate after first vring_more_used()..?
> 
> vring_get_buf last_used_idx: 0 vr: 0x000ed404 vr->num: 1
> vring_get_buf checking &used->ring[0]
> vring_get_buf, using new last_unsed: 0 >>>>>>>>>>>>>>>>>>
> vring_get_buf using id: 0 from elem->id: 0x000ed004
> vring_detach: vq->free_head: 3
> vring_detach: Setting new vq->free_head: 0
> virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 1
> Calling virtio_scsi_scan_target for target: 1
> Searching bootorder for: /pci at i0cf8/*@4/*@0/*@1,0
> virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2
> virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 1
> vring_add_buf, vr: 0x000ed404 vr->num: 1
> vring_add_buf, head: 0, index: 0
> vring_add_buf, setting desc[prev=2].flags
> vring_add_buf, setting free_head: 3
> vring_add_buf, setting q->vdata[head=0]
> vring_add_buf, setting q->ring[av=0]
> virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 1
> virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 1
> virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 2
>                                           ^^^^^^^^^^^^^^^^^^^^^^^^^
> 
>   Incremented from 1 to 2 after second vring_more_used()..?
> 
> vring_get_buf last_used_idx: 1 vr: 0x000ed404 vr->num: 2
> vring_get_buf checking &used->ring[1]
> vring_get_buf, using new last_unsed: 1 >>>>>>>>>>>>>>>>>>
> vring_get_buf using id: 0 from elem->id: 0x000ed00c
> vring_detach: vq->free_head: 3
> vring_detach: Setting new vq->free_head: 0
> virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 2
> virtio-scsi vendor='LIO-ORG' product='RAMDISK-MCP' rev='4.0' type=0 removable=0
> virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 1
> virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 2
> vring_add_buf, vr: 0x000ed404 vr->num: 2
> vring_add_buf, head: 0, index: 0
> vring_add_buf, setting desc[prev=1].flags
> vring_add_buf, setting free_head: 2
> vring_add_buf, setting q->vdata[head=0]
> vring_add_buf, setting q->ring[av=0]
> virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 2
> virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 2
> virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 3
>                                           ^^^^^^^^^^^^^^^^^^^^^^^^^
> 
>   Incremented from 2 to 3, and so on..
> 
> and this keeps happening until vr->num begins to exceed
> MAX_QUEUE_NUM around scanning of target ID 127:
> 
> virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 128
> virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 128
> virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 129
> vring_get_buf last_used_idx: 128 vr: 0x000ed404 vr->num: 129
> vring_get_buf checking &used->ring[128]
> vring_get_buf, using new last_unsed: 128 >>>>>>>>>>>>>>>>>>
> vring_get_buf using id: 129 from elem->id: 0x000ed404
> vring_detach: vq->free_head: 3
> vring_detach: Setting new vq->free_head: 129
> virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 129
> Calling virtio_scsi_scan_target for target: 127
> Searching bootorder for: /pci at i0cf8/*@4/*@0/*@127,0
> virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2
> virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 129
> vring_add_buf, vr: 0x000ed404 vr->num: 129
> vring_add_buf, head: 129, index: 0
> vring_add_buf, setting desc[prev=4].flags
> vring_add_buf, setting free_head: 5
> vring_add_buf, setting q->vdata[head=0]
> vring_add_buf, setting q->ring[av=129]
> virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 129
> virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 129
> virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 130
> vring_get_buf last_used_idx: 129 vr: 0x000ed404 vr->num: 130
> vring_get_buf checking &used->ring[129]
> vring_get_buf, using new last_unsed: 129 >>>>>>>>>>>>>>>>>>
> vring_get_buf using id: 968704 from elem->id: 0x000ed40c
> vring_detach: vq->free_head: 5
> vring_detach: Setting new vq->free_head: 968704
> virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 130
> Calling virtio_scsi_scan_target for target: 128
> Searching bootorder for: /pci at i0cf8/*@4/*@0/*@128,0
> virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2
> virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 130
> vring_add_buf, vr: 0x000ed404 vr->num: 130
> vring_add_buf, head: 51200, index: 0
> vring_add_buf, setting desc[prev=1].flags
> vring_add_buf, setting free_head: 2
> vring_add_buf, setting q->vdata[head=0]
> vring_add_buf, setting q->ring[av=51200]
> 
> until '[17348.044031] Invalid buffer layout out: 0 in: 2' appears on the
> vhost.
> 
> So it's clear this definitely is not supposed to be happening, but I've
> not yet been able to ascertain why it's suddenly being triggered now..?
> I don't recall Asias running into a similar issue during his earlier
> testing, but this bug is happening after every I/O in SeaBIOS with the
> most recent vhost-scsi-pci code.
> 
> I'm using the following to work-around this issue for the moment, and
> would like some input from virtio / SeaBIOS folks..
> 
> WDYT..?
> 
> --nab
> 
> diff --git a/src/virtio-ring.c b/src/virtio-ring.c
> index bddb090..e046141 100644
> --- a/src/virtio-ring.c
> +++ b/src/virtio-ring.c
> @@ -35,10 +35,16 @@
>  
>  int vring_more_used(struct vring_virtqueue *vq)
>  {
> +    struct vring *vr = &vq->vring;
>      struct vring_used *used = GET_LOWFLAT(vq->vring.used);
>      int more = GET_LOWFLAT(vq->last_used_idx) != GET_LOWFLAT(used->idx);
>      /* Make sure ring reads are done after idx read above. */
>      smp_rmb();
> +
> +    /* Huh..?  vr->num is somehow changing from below us..? */
> +    if (GET_LOWFLAT(vr->num) != MAX_QUEUE_NUM) {
> +           SET_LOWFLAT(vr->num, MAX_QUEUE_NUM);
> +    }
>      return more;
>  }
> 
> --
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