net: ethtool: let drivers remove lost RSS contexts

RSS contexts may get lost from a device, in various extreme circumstances.
Specifically if the firmware leaks resources and resets, or crashes and
either recovers in partially working state or the crash causes a
different FW version to run - creating the context again may fail.

Drivers should do their absolute best to prevent this from happening.
When it does, however, telling user that a context exists, when it can't
possibly be used any more is counter productive. Add a helper for
drivers to discard contexts. Print an error, in the future netlink
notification will also be sent.

More robust approaches were proposed, like keeping the contexts
but marking them as "dead" (but possibly resurrected by next reset).
That may be better but it's unclear at this stage whether the
effort is worth the benefits.
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20240711220713.283778-2-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/ethtool.h

@@ -210,6 +210,8 @@ static inline size_t ethtool_rxfh_context_size(u32 indir_size, u32 key_size,
 	return struct_size_t(struct ethtool_rxfh_context, data, flex_len);
 }
 
+void ethtool_rxfh_context_lost(struct net_device *dev, u32 context_id);
+
 /* declare a link mode bitmap */
 #define __ETHTOOL_DECLARE_LINK_MODE_MASK(name)		\
 	DECLARE_BITMAP(name, __ETHTOOL_LINK_MODE_MASK_NBITS)

net/ethtool/common.c

@@ -741,3 +741,17 @@ ethtool_forced_speed_maps_init(struct ethtool_forced_speed_map *maps, u32 size)
 	}
 }
 EXPORT_SYMBOL_GPL(ethtool_forced_speed_maps_init);
+
+void ethtool_rxfh_context_lost(struct net_device *dev, u32 context_id)
+{
+	struct ethtool_rxfh_context *ctx;
+
+	WARN_ONCE(!rtnl_is_locked() &&
+		  !lockdep_is_held_type(&dev->ethtool->rss_lock, -1),
+		  "RSS context lock assertion failed\n");
+
+	netdev_err(dev, "device error, RSS context %d lost\n", context_id);
+	ctx = xa_erase(&dev->ethtool->rss_ctx, context_id);
+	kfree(ctx);
+}
+EXPORT_SYMBOL(ethtool_rxfh_context_lost);