Re: [PATCH net] net: mana: do not discard an ethtool-configured RSS table on a queue rebuild
flat view
From: Jakub Kicinski <kuba@kernel.org>
Date: 2026-09-10 15:18:18
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linux-hyperv, linux-rdma, lkml
On Fri, 4 Sep 2026 17:44:01 -0700 Long Li wrote:
mana_alloc_queues() regenerates the RSS indirection table from the driver
default every time the queues are built, so a table installed with
"ethtool -X" is silently replaced by any operation that rebuilds them:
an MTU change, a ring-size, channel-count or private-flag change, an XDP
attach, TX-timeout reset recovery, or resume.
The driver never clears the core's IFF_RXFH_CONFIGURED, so
netif_is_rxfh_configured() keeps reporting a user table while the
hardware has been reprogrammed with the default one. "ethtool -x" then
shows a table the user did not ask for, with no indication it changed:
# ethtool -X ens1 equal 2
# ethtool -x ens1
RX flow hash indirection table for ens1 with 16 RX ring(s):
0: 0 1 0 1 0 1 0 1
8: 0 1 0 1 0 1 0 1
# ip link set ens1 mtu 1400
# ethtool -x ens1
RX flow hash indirection table for ens1 with 16 RX ring(s):
0: 0 1 2 3 4 5 6 7
8: 8 9 10 11 12 13 14 15
Keep the table instead, and rebuild it only when it is driver-generated
or cannot be honoured. An entry may not be kept if it points past the
last queue: mana_config_rss() uses these entries to index apc->rxqs[],
which holds apc->num_queues pointers. That is reachable because
mana_attach() calls mana_init_port(), which lowers apc->num_queues to the
maximum the device reports, so a table configured for more queues can
outlive them.To be clear this is only acceptable if the number of queues drops due to re-negotiation of caps with the device, not for example if XDP requires some queues to be used for other purposes. In the latter case just refuse the config change.
A table that cannot be kept is still replaced by the default silently, without ethtool_rxfh_indir_lost(). That helper sends ETHTOOL_MSG_RSS_NTF, which requires the netdev instance lock, and mana_alloc_queues() runs both with that lock held, from ndo_open, and without it, from mana_attach() on the reset and resume paths. Leaving the core's view untouched is what the driver did for every table before this change.
Okay, so you have a problem of not having the lock...
Opt the RSS ethtool operations into rtnl_lock() while here. Reading the table in mana_alloc_queues() has to be serialized against mana_set_rxfh() replacing it, and the two had no lock in common: mana_set_rxfh() ran under the netdev instance lock alone, while mana_alloc_queues() reaches this point holding only RTNL, from ndo_open and from mana_attach() on the reset and resume paths. Taking the instance lock there instead is not possible, since ndo_open already runs with it held. The same flag covers the netlink and ioctl entry points.
.. and yet your fix is not to try to take it but the reverse, to add a different lock? You need to explain why reset path can't take the instance lock. Of course you can't take it _inside_ ndo_open, but the caller should be able to.
quoted hunk ↗ jump to hunk
Fixes: ca9c54d2d6a5 ("net: mana: Add a driver for Microsoft Azure Network Adapter (MANA)") Signed-off-by: Long Li <longli@microsoft.com> --- drivers/net/ethernet/microsoft/mana/mana_en.c | 37 ++++++++++++++++++- .../ethernet/microsoft/mana/mana_ethtool.c | 3 +- 2 files changed, 38 insertions(+), 2 deletions(-)diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c index 7a1ac853e3abcd28c4a1e5c6987ec631a18ad840..97386e17b9421aedefa25bab6fbf0b7b1f2996d4 100644 --- a/drivers/net/ethernet/microsoft/mana/mana_en.c +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c@@ -3306,6 +3306,28 @@ static void mana_rss_table_init(struct mana_port_context *apc) ethtool_rxfh_indir_default(i, apc->num_queues); } +/* Whether the current indirection table can be kept for apc->num_queues, + * rather than rebuilt from the driver default. + * + * Only a user table ("ethtool -X") is worth keeping; a driver-generated one + * is rebuilt so that it spreads over every queue. An entry pointing past the + * last queue cannot be kept: mana_config_rss() uses these entries to index + * apc->rxqs[], which holds apc->num_queues pointers. + */ +static bool mana_rss_table_keep(struct mana_port_context *apc) +{ + u32 i; + + if (!netif_is_rxfh_configured(apc->ndev)) + return false; + + for (i = 0; i < apc->indir_table_sz; i++) + if (apc->indir_table[i] >= apc->num_queues) + return false; + + return true; +} + int mana_disable_vport_rx(struct mana_port_context *apc) { return mana_cfg_vport_steering(apc, TRI_STATE_FALSE, false, false,@@ -3621,7 +3643,20 @@ int mana_alloc_queues(struct net_device *ndev) goto destroy_rxq; } - mana_rss_table_init(apc); + /* Keep a user-configured table across the rebuild: its entries are + * queue indices and stay meaningful while they are all still in range. + * Only a driver-generated table is regenerated here. + * + * A table that cannot be kept is replaced by the default without + * telling the core, which keeps reporting the table as user + * configured. That is what this function did for every table before, + * and reporting it here is not an option: ethtool_rxfh_indir_lost() + * sends ETHTOOL_MSG_RSS_NTF, which requires the netdev instance lock, + * and this runs both with that lock held (ndo_open) and without it + * (mana_attach() from the reset and resume paths). + */ + if (!mana_rss_table_keep(apc)) + mana_rss_table_init(apc); err = mana_config_rss(apc, TRI_STATE_TRUE, true, true); if (err) {diff --git a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c index ece7ff9cc409a806b6a6de70a85b44874bfa6dad..e3acaf17efabcd62f7cffabdb8404cf16b917272 100644 --- a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c +++ b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c@@ -871,7 +871,8 @@ const struct ethtool_ops mana_ethtool_ops = { .op_needs_rtnl = ETHTOOL_OP_NEEDS_RTNL_SCHANNELS | ETHTOOL_OP_NEEDS_RTNL_SRINGPARAM | ETHTOOL_OP_NEEDS_RTNL_SPFLAGS | - ETHTOOL_OP_NEEDS_RTNL_GLINK, + ETHTOOL_OP_NEEDS_RTNL_GLINK | + ETHTOOL_OP_NEEDS_RTNL_RSS, .get_ethtool_stats = mana_get_ethtool_stats, .get_sset_count = mana_get_sset_count, .get_strings = mana_get_strings,