Merge branch 'net-netpoll-fix-memory-leak-and-add-comprehensive-selftests'

Breno Leitao says:

====================
net: netpoll: fix memory leak and add comprehensive selftests

Fix a memory leak in netpoll and introduce netconsole selftests that
expose the issue when running with kmemleak detection enabled.

This patchset includes a selftest for netpoll with multiple concurrent
users (netconsole + bonding), which simulates the scenario from test[1]
that originally demonstrated the issue allegedly fixed by commit
efa95b0 ("netpoll: fix use after free") - a commit that is now
being reverted.

Sending this to "net" branch because this is a fix, and the selftest
might help with the backports validation.

Link: https://lore.kernel.org/lkml/96b940137a50e5c387687bb4f57de8b0435a653f.1404857349.git.decot@googlers.com/ [1]
====================

Link: https://patch.msgid.link/20251107-netconsole_torture-v10-0-749227b55f63@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/core/netpoll.c

@@ -811,6 +811,10 @@ static void __netpoll_cleanup(struct netpoll *np)
 	if (!npinfo)
 		return;
 
+	/* At this point, there is a single npinfo instance per netdevice, and
+	 * its refcnt tracks how many netpoll structures are linked to it. We
+	 * only perform npinfo cleanup when the refcnt decrements to zero.
+	 */
 	if (refcount_dec_and_test(&npinfo->refcnt)) {
 		const struct net_device_ops *ops;
 
@@ -820,8 +824,7 @@ static void __netpoll_cleanup(struct netpoll *np)
 
 		RCU_INIT_POINTER(np->dev->npinfo, NULL);
 		call_rcu(&npinfo->rcu, rcu_cleanup_netpoll_info);
-	} else
-		RCU_INIT_POINTER(np->dev->npinfo, NULL);
+	}
 
 	skb_pool_flush(np);
 }

tools/testing/selftests/drivers/net/Makefile

@@ -18,6 +18,7 @@ TEST_PROGS := \
 	netcons_fragmented_msg.sh \
 	netcons_overflow.sh \
 	netcons_sysdata.sh \
+	netcons_torture.sh \
 	netpoll_basic.py \
 	ping.py \
 	psp.py \

tools/testing/selftests/drivers/net/bonding/Makefile

@@ -14,6 +14,7 @@ TEST_PROGS := \
 	dev_addr_lists.sh \
 	mode-1-recovery-updelay.sh \
 	mode-2-recovery-updelay.sh \
+	netcons_over_bonding.sh \
 # end of TEST_PROGS
 
 TEST_FILES := \
@@ -24,6 +25,7 @@ TEST_FILES := \
 
 TEST_INCLUDES := \
 	../../../net/lib.sh \
+	../lib/sh/lib_netcons.sh \
 	../../../net/forwarding/lib.sh \
 # end of TEST_INCLUDES
 

tools/testing/selftests/drivers/net/bonding/config

@@ -1,5 +1,6 @@
 CONFIG_BONDING=y
 CONFIG_BRIDGE=y
+CONFIG_CONFIGFS_FS=y
 CONFIG_DUMMY=y
 CONFIG_INET_ESP=y
 CONFIG_INET_ESP_OFFLOAD=y
@@ -9,6 +10,9 @@ CONFIG_MACVLAN=y
 CONFIG_NET_ACT_GACT=y
 CONFIG_NET_CLS_FLOWER=y
 CONFIG_NET_CLS_MATCHALL=m
+CONFIG_NETCONSOLE=m
+CONFIG_NETCONSOLE_DYNAMIC=y
+CONFIG_NETCONSOLE_EXTENDED_LOG=y
 CONFIG_NETDEVSIM=m
 CONFIG_NET_SCH_INGRESS=y
 CONFIG_NLMON=y