On 22 Mar 2022, at 13:04, Tao Liu wrote:
> If netdev goes away(i.e. qemu with a vnet shutdown), kernel delete all tc
> filters, those tcf_id related to the netdev will be left in ufid_to_tc
> hashmap.
> When qemu restart with a same vnet but different ifindex assigned,
> a dup ufid may add. Especially after hashmap_expand, the old entry will
> insert before the new one, delete or modify tc flow will always fail.
>
> So delete the stale entry to avoid a duplicated ufid in hashmap.
There are some comments below, as I still do not fully understand the fix.
> Fixes: dd8ca104acd7 ("netdev-tc-offloads: Don't delete ufid mapping if fail
> to delete filter")))
> Signed-off-by: Tao Liu <[email protected]>
> ---
> lib/netdev-offload-tc.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/lib/netdev-offload-tc.c b/lib/netdev-offload-tc.c
> index 12d0a9af3..e9dd66790 100644
> --- a/lib/netdev-offload-tc.c
> +++ b/lib/netdev-offload-tc.c
> @@ -167,6 +167,9 @@ struct ufid_tc_data {
> struct netdev *netdev;
> };
>
> +static void parse_tc_flower_to_stats(struct tc_flower *flower,
> + struct dpif_flow_stats *stats);
> +
> static void
> del_ufid_tc_mapping_unlocked(const ovs_u128 *ufid)
> {
> @@ -200,11 +203,24 @@ del_ufid_tc_mapping(const ovs_u128 *ufid)
>
> /* Wrapper function to delete filter and ufid tc mapping */
> static int
> -del_filter_and_ufid_mapping(struct tcf_id *id, const ovs_u128 *ufid)
> +del_filter_and_ufid_mapping(struct tcf_id *id, const ovs_u128 *ufid,
> + struct dpif_flow_stats *stats)
> {
> - int err;
> + struct tc_flower flower;
> + int err = 0, get_err;
> +
> + get_err = tc_get_flower(id, &flower);
> + if (!get_err) {
We should definitely add a comment here explaining the reasoning behind doing
the get first and then the delete!
However, it’s still not clear to me why this change does not undo, dd8ca104acd7?
Because tc_get_flower() just finds out if the entry with the ID exists in the
kernel, and than only try to delete it.
For this can you just not check a specific return value in the tc_del_filter()
call?
I assume dd8ca104acd7 just want to skip removing the del_ufid_tc_mapping() if
the entry does NOT exist in the kernel?
If not maybe Jianbo can explain a bit more the corner case, or maybe has a test
case for this?
> + err = tc_del_filter(id);
> + }
> +
> + if (stats) {
> + memset(stats, 0, sizeof *stats);
> + if (!get_err) {
> + parse_tc_flower_to_stats(&flower, stats);
> + }
> + }
I guess this was moved here to avoid the additional tc_get_flower() call below.
I would fold the stats part in the above if() case to avoid the need for the
get_err variable, i.e.
if (!tc_get_flower(id, &flower)) {
err = tc_del_filter(id);
if (stats) {
memset(stats, 0, sizeof *stats);
if (!get_err) {
parse_tc_flower_to_stats(&flower, stats);
}
}
>
> - err = tc_del_filter(id);
> if (!err) {
> del_ufid_tc_mapping(ufid);
> }
> @@ -1946,7 +1962,8 @@ netdev_tc_flow_put(struct netdev *netdev, struct match
> *match,
> if (get_ufid_tc_mapping(ufid, &id) == 0) {
> VLOG_DBG_RL(&rl, "updating old handle: %d prio: %d",
> id.handle, id.prio);
> - info->tc_modify_flow_deleted = !del_filter_and_ufid_mapping(&id,
> ufid);
> + info->tc_modify_flow_deleted =
> + !del_filter_and_ufid_mapping(&id, ufid, NULL);
> }
>
> prio = get_prio_for_tc_flower(&flower);
> @@ -2017,7 +2034,6 @@ netdev_tc_flow_del(struct netdev *netdev OVS_UNUSED,
> const ovs_u128 *ufid,
> struct dpif_flow_stats *stats)
> {
> - struct tc_flower flower;
> struct tcf_id id;
> int error;
>
> @@ -2026,16 +2042,7 @@ netdev_tc_flow_del(struct netdev *netdev OVS_UNUSED,
> return error;
> }
>
> - if (stats) {
> - memset(stats, 0, sizeof *stats);
> - if (!tc_get_flower(&id, &flower)) {
> - parse_tc_flower_to_stats(&flower, stats);
> - }
> - }
> -
> - error = del_filter_and_ufid_mapping(&id, ufid);
> -
> - return error;
> + return del_filter_and_ufid_mapping(&id, ufid, stats);
> }
>
> static int
> --
> 2.23.0
>
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