On Wed, 27 Nov 2024 10:09:53 +0100
Laurent Vivier <lvivier(a)redhat.com> wrote:
On 27/11/2024 05:47, Stefano Brivio wrote:
> On Fri, 22 Nov 2024 17:43:34 +0100
> Laurent Vivier <lvivier(a)redhat.com> wrote:
>
>> +/**
>> + * tcp_vu_send_flag() - Send segment with flags to vhost-user (no payload)
>> + * @c: Execution context
>> + * @conn: Connection pointer
>> + * @flags: TCP flags: if not set, send segment only if ACK is due
>> + *
>> + * Return: negative error code on connection reset, 0 otherwise
>> + */
>> +int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
>> +{
>> + struct vu_dev *vdev = c->vdev;
>> + struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
>> + const struct flowside *tapside = TAPFLOW(conn);
>> + size_t l2len, l4len, optlen, hdrlen;
>> + struct vu_virtq_element flags_elem[2];
>> + struct tcp_payload_t *payload;
>> + struct ipv6hdr *ip6h = NULL;
>> + struct iovec flags_iov[2];
>> + struct iphdr *iph = NULL;
>> + struct ethhdr *eh;
>> + uint32_t seq;
>> + int elem_cnt;
>> + int nb_ack;
>> + int ret;
>> +
>> + hdrlen = tcp_vu_hdrlen(CONN_V6(conn));
>> +
>> + vu_set_element(&flags_elem[0], NULL, &flags_iov[0]);
>> +
>> + elem_cnt = vu_collect(vdev, vq, &flags_elem[0], 1,
>> + hdrlen + sizeof(struct tcp_syn_opts), NULL);
>
> Oops, I made this crash, by starting a number of iperf3 client threads
> on the host:
>
> $ iperf3 -c localhost -p 6001 -Z -l 500 -w 256M -t 600 -P20
>
> with matching server in the guest, then terminating QEMU while the test
> is running.
>
> Details (I saw it first, then I reproduced it under gdb):
>
> accepted connection from PID 3115463
> NDP: received RS, sending RA
> DHCP: offer to discover
> from 52:54:00:12:34:56
> DHCP: ack to request
> from 52:54:00:12:34:56
> NDP: sending unsolicited RA, next in 212s
> Client connection closed
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00005555555884f5 in vring_avail_idx (vq=0x555559343f10 <vdev_storage+1296>)
at virtio.c:138
> 138 vq->shadow_avail_idx = le16toh(vq->vring.avail->idx);
> (gdb) list
> 133 *
> 134 * Return: the available ring index of the given virtqueue
> 135 */
> 136 static inline uint16_t vring_avail_idx(struct vu_virtq *vq)
> 137 {
> 138 vq->shadow_avail_idx = le16toh(vq->vring.avail->idx);
> 139
> 140 return vq->shadow_avail_idx;
> 141 }
> 142
> (gdb) bt
> #0 0x00005555555884f5 in vring_avail_idx (vq=0x555559343f10
<vdev_storage+1296>) at virtio.c:138
> #1 vu_queue_empty (vq=vq@entry=0x555559343f10 <vdev_storage+1296>) at
virtio.c:290
> #2 vu_queue_pop (dev=dev@entry=0x555559343a00 <vdev_storage>,
vq=vq@entry=0x555559343f10 <vdev_storage+1296>, elem=elem@entry=0x7ffffff6f510) at
virtio.c:505
> #3 0x0000555555588c8c in vu_collect (vdev=vdev@entry=0x555559343a00
<vdev_storage>, vq=vq@entry=0x555559343f10 <vdev_storage+1296>,
elem=elem@entry=0x7ffffff6f510, max_elem=max_elem@entry=1,
> size=size@entry=74, frame_size=frame_size@entry=0x0) at vu_common.c:86
> #4 0x000055555557e00e in tcp_vu_send_flag (c=0x7ffffff6f7a0, conn=0x5555555bd2d0
<flowtab+2160>, flags=4) at tcp_vu.c:116
> #5 0x0000555555578125 in tcp_send_flag (flags=4, conn=0x5555555bd2d0
<flowtab+2160>, c=0x7ffffff6f7a0) at tcp.c:1278
> #6 tcp_rst_do (conn=<optimized out>, c=<optimized out>) at tcp.c:1293
> #7 tcp_timer_handler (c=c@entry=0x7ffffff6f7a0, ref=..., ref@entry=...) at
tcp.c:2266
> #8 0x0000555555558f26 in main (argc=<optimized out>, argv=<optimized
out>) at passt.c:342
> (gdb) p *vq
> $1 = {vring = {num = 256, desc = 0x0, avail = 0x0, used = 0x0, log_guest_addr =
4338774592, flags = 0}, last_avail_idx = 35133, shadow_avail_idx = 35133, used_idx =
35133, signalled_used = 0,
> signalled_used_valid = false, notification = true, inuse = 0, call_fd = -1,
kick_fd = -1, err_fd = -1, enable = 1, started = false, vra = {index = 0, flags = 0,
desc_user_addr = 139660501995520,
> used_user_addr = 139660502000192, avail_user_addr = 139660501999616,
log_guest_addr = 4338774592}}
> (gdb) p *vq->vring.avail
> Cannot access memory at address 0x0
>
> ...so we're sending a RST segment to the guest, but the ring doesn't
> exist anymore.
>
> By the way, I still have the gdb session running, if you need something
> else out of it.
>
> Now, I guess we should eventually introduce a more comprehensive
> handling of the case where the guest suddenly terminates (not specific
> to vhost-user), but given that we have vu_cleanup() working as expected
> in this case, I wonder if we shouldn't simply avoid calling
> vring_avail_idx() (it has a single caller) by checking for !vring.avail
> in the caller, or something like that.
>
Yes, I think it's the lines I removed during the reviews:
if (!vq->vring.avail)
return true;
Ah, right:
https://archives.passt.top/passt-dev/20241114163859.7eeafa38@elisabeth/
...so, at least in our case, it's more than "sanity checks" after all.
:) Well, I guess it depends on the definition.
Could you try to checkout virtio.c from v11?
That would take a rather lengthy rebase, but I tried to reintroduce all
the checks you had:
--
diff --git a/virtio.c b/virtio.c
index 6a97435..0598ff4 100644
--- a/virtio.c
+++ b/virtio.c
@@ -284,6 +284,9 @@ static int virtqueue_read_next_desc(const struct vring_desc *desc,
*/
bool vu_queue_empty(struct vu_virtq *vq)
{
+ if (!vq->vring.avail)
+ return true;
+
if (vq->shadow_avail_idx != vq->last_avail_idx)
return false;
@@ -327,6 +330,9 @@ static bool vring_can_notify(const struct vu_dev *dev, struct
vu_virtq *vq)
*/
void vu_queue_notify(const struct vu_dev *dev, struct vu_virtq *vq)
{
+ if (!vq->vring.avail)
+ return;
+
if (!vring_can_notify(dev, vq)) {
debug("vhost-user: virtqueue can skip notify...");
return;
@@ -502,6 +508,9 @@ int vu_queue_pop(struct vu_dev *dev, struct vu_virtq *vq, struct
vu_virtq_elemen
unsigned int head;
int ret;
+ if (!vq->vring.avail)
+ return -1;
+
if (vu_queue_empty(vq))
return -1;
@@ -591,6 +600,9 @@ void vu_queue_fill_by_index(struct vu_virtq *vq, unsigned int index,
{
struct vring_used_elem uelem;
+ if (!vq->vring.avail)
+ return;
+
idx = (idx + vq->used_idx) % vq->vring.num;
uelem.id = htole32(index);
@@ -633,6 +645,9 @@ void vu_queue_flush(struct vu_virtq *vq, unsigned int count)
{
uint16_t old, new;
+ if (!vq->vring.avail)
+ return;
+
/* Make sure buffer is written before we update index. */
smp_wmb();
--
and it's all fine with those, I tried doing a few nasty things and
didn't observe any issue.
Any check I missed? Do you want to submit it as follow-up patch? I can
also do that. I'd rather (still) avoid a re-post of v14 if possible.
As you prefer. Let me know.