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SubjectRe: linux-next: build failure after merge of the net-next tree
From
From: Stephen Rothwell <sfr@canb.auug.org.au>
Date: Fri, 10 Jan 2020 10:57:38 +1100

> After merging the net-next tree, today's linux-next build (x86_64
> allmodconfig) failed like this:
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> index 17b29e2d19ed..54807b4930fe 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> @@ -767,7 +767,7 @@ __mlxsw_sp_qdisc_ets_graft(struct mlxsw_sp_port *mlxsw_sp_port,
> mlxsw_sp_port->tclass_qdiscs[tclass_num].handle == child_handle)
> return 0;
>
> - if (!p->child_handle) {
> + if (!child_handle) {
> /* This is an invisible FIFO replacing the original Qdisc.
> * Ignore it--the original Qdisc's destroy will follow.
> */
> --
> 2.24.0

Yep, this is the merge resolution you will find in net-next at commit:

commit a2d6d7ae591c47ebc04926cb29a840adfdde49e6
Merge: b1daa4d19473 e69ec487b2c7
Author: David S. Miller <davem@davemloft.net>
Date: Thu Jan 9 12:10:26 2020 -0800

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

The ungrafting from PRIO bug fixes in net, when merged into net-next,
merge cleanly but create a build failure. The resolution used here is
from Petr Machata.

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
index 81a2c087f534,46d43cfd04e9..54807b4930fe
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
@@@ -681,92 -631,33 +681,99 @@@ static struct mlxsw_sp_qdisc_ops mlxsw_
.clean_stats = mlxsw_sp_setup_tc_qdisc_prio_clean_stats,
};

-/* Grafting is not supported in mlxsw. It will result in un-offloading of the
- * grafted qdisc as well as the qdisc in the qdisc new location.
- * (However, if the graft is to the location where the qdisc is already at, it
- * will be ignored completely and won't cause un-offloading).
+static int
+mlxsw_sp_qdisc_ets_check_params(struct mlxsw_sp_port *mlxsw_sp_port,
+ struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
+ void *params)
+{
+ struct tc_ets_qopt_offload_replace_params *p = params;
+
+ return __mlxsw_sp_qdisc_ets_check_params(p->bands);
+}
+
+static int
+mlxsw_sp_qdisc_ets_replace(struct mlxsw_sp_port *mlxsw_sp_port,
+ struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
+ void *params)
+{
+ struct tc_ets_qopt_offload_replace_params *p = params;
+
+ return __mlxsw_sp_qdisc_ets_replace(mlxsw_sp_port, p->bands,
+ p->quanta, p->weights, p->priomap);
+}
+
+static void
+mlxsw_sp_qdisc_ets_unoffload(struct mlxsw_sp_port *mlxsw_sp_port,
+ struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
+ void *params)
+{
+ struct tc_ets_qopt_offload_replace_params *p = params;
+
+ __mlxsw_sp_qdisc_ets_unoffload(mlxsw_sp_port, mlxsw_sp_qdisc,
+ p->qstats);
+}
+
+static int
+mlxsw_sp_qdisc_ets_destroy(struct mlxsw_sp_port *mlxsw_sp_port,
+ struct mlxsw_sp_qdisc *mlxsw_sp_qdisc)
+{
+ return __mlxsw_sp_qdisc_ets_destroy(mlxsw_sp_port);
+}
+
+static struct mlxsw_sp_qdisc_ops mlxsw_sp_qdisc_ops_ets = {
+ .type = MLXSW_SP_QDISC_ETS,
+ .check_params = mlxsw_sp_qdisc_ets_check_params,
+ .replace = mlxsw_sp_qdisc_ets_replace,
+ .unoffload = mlxsw_sp_qdisc_ets_unoffload,
+ .destroy = mlxsw_sp_qdisc_ets_destroy,
+ .get_stats = mlxsw_sp_qdisc_get_prio_stats,
+ .clean_stats = mlxsw_sp_setup_tc_qdisc_prio_clean_stats,
+};
+
+/* Linux allows linking of Qdiscs to arbitrary classes (so long as the resulting
+ * graph is free of cycles). These operations do not change the parent handle
+ * though, which means it can be incomplete (if there is more than one class
+ * where the Qdisc in question is grafted) or outright wrong (if the Qdisc was
+ * linked to a different class and then removed from the original class).
+ *
+ * E.g. consider this sequence of operations:
+ *
+ * # tc qdisc add dev swp1 root handle 1: prio
+ * # tc qdisc add dev swp1 parent 1:3 handle 13: red limit 1000000 avpkt 10000
+ * RED: set bandwidth to 10Mbit
+ * # tc qdisc link dev swp1 handle 13: parent 1:2
+ *
+ * At this point, both 1:2 and 1:3 have the same RED Qdisc instance as their
+ * child. But RED will still only claim that 1:3 is its parent. If it's removed
+ * from that band, its only parent will be 1:2, but it will continue to claim
+ * that it is in fact 1:3.
+ *
+ * The notification for child Qdisc replace (e.g. TC_RED_REPLACE) comes before
+ * the notification for parent graft (e.g. TC_PRIO_GRAFT). We take the replace
+ * notification to offload the child Qdisc, based on its parent handle, and use
+ * the graft operation to validate that the class where the child is actually
+ * grafted corresponds to the parent handle. If the two don't match, we
+ * unoffload the child.
*/
static int
-mlxsw_sp_qdisc_prio_graft(struct mlxsw_sp_port *mlxsw_sp_port,
- struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
- struct tc_prio_qopt_offload_graft_params *p)
+__mlxsw_sp_qdisc_ets_graft(struct mlxsw_sp_port *mlxsw_sp_port,
+ struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
+ u8 band, u32 child_handle)
{
- int tclass_num = MLXSW_SP_PRIO_BAND_TO_TCLASS(p->band);
+ int tclass_num = MLXSW_SP_PRIO_BAND_TO_TCLASS(band);
struct mlxsw_sp_qdisc *old_qdisc;

- /* Check if the grafted qdisc is already in its "new" location. If so -
- * nothing needs to be done.
- */
- if (p->band < IEEE_8021QAZ_MAX_TCS &&
- mlxsw_sp_port->tclass_qdiscs[tclass_num].handle == p->child_handle)
+ if (band < IEEE_8021QAZ_MAX_TCS &&
+ mlxsw_sp_port->tclass_qdiscs[tclass_num].handle == child_handle)
return 0;

- if (!p->child_handle) {
++ if (!child_handle) {
+ /* This is an invisible FIFO replacing the original Qdisc.
+ * Ignore it--the original Qdisc's destroy will follow.
+ */
+ return 0;
+ }
+
/* See if the grafted qdisc is already offloaded on any tclass. If so,
* unoffload it.
*/

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