Switching back to the 5.10 kernel, I ran kmemleak, cleared the boot log to eliminate potentially false positives, then ran a scan.
root@OpenWrt:~# cat /sys/kernel/debug/kmemleak | tee memleakoutput.txt
unreferenced object 0x800000000558e800 (size 512):
comm "swapper/0", pid 1, jiffies 4294937838 (age 483.240s)
hex dump (first 32 bytes):
6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
backtrace:
[<0000000092547866>] __kmalloc+0x1c4/0x768
[<000000002902bd0d>] cvm_oct_mem_fill_fpa+0x60/0x1a8
[<0000000016c62570>] cvm_oct_probe+0xa4/0xab8
[<00000000bdc4ede7>] platform_drv_probe+0x28/0x88
[<00000000a567e8b8>] really_probe+0xfc/0x4e0
[<0000000096837a2a>] device_driver_attach+0x120/0x130
[<00000000ec1cb103>] __driver_attach+0x7c/0x148
[<00000000fb6265da>] bus_for_each_dev+0x68/0xa8
[<000000004feb0e7d>] bus_add_driver+0x1d0/0x218
[<0000000069658853>] driver_register+0x98/0x160
[<00000000cec7f896>] do_one_initcall+0x54/0x168
[<0000000035c2e6f9>] kernel_init_freeable+0x280/0x31c
[<0000000046a35530>] kernel_init+0x14/0x104
[<00000000991d0df4>] ret_from_kernel_thread+0x14/0x1c
unreferenced object 0x80000000052de480 (size 216):
comm "softirq", pid 0, jiffies 4294960228 (age 259.360s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<0000000078af28d6>] kmem_cache_alloc+0x1ac/0x708
[<000000001d074ea2>] __build_skb+0x34/0xd8
[<00000000339b0f83>] __netdev_alloc_skb+0x118/0x1f0
[<00000000db3556b0>] cvm_oct_mem_fill_fpa+0x154/0x1a8
[<00000000a49e80de>] cvm_oct_napi_poll+0x4c0/0x988
[<00000000d0c3cba0>] __napi_poll+0x3c/0x158
[<00000000bb0c10eb>] net_rx_action+0xe8/0x210
[<000000003322eb9f>] __do_softirq+0x168/0x360
[<00000000d4037fcb>] irq_exit+0x9c/0xe8
[<00000000224da306>] plat_irq_dispatch+0x48/0xd0
[<00000000327ba56b>] handle_int+0x14c/0x158
[<000000003eae4681>] __r4k_wait+0x20/0x40
unreferenced object 0x80000000052ddb80 (size 216):
comm "softirq", pid 0, jiffies 4294960228 (age 259.360s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<0000000078af28d6>] kmem_cache_alloc+0x1ac/0x708
[<000000001d074ea2>] __build_skb+0x34/0xd8
[<00000000339b0f83>] __netdev_alloc_skb+0x118/0x1f0
[<00000000db3556b0>] cvm_oct_mem_fill_fpa+0x154/0x1a8
[<00000000a49e80de>] cvm_oct_napi_poll+0x4c0/0x988
[<00000000d0c3cba0>] __napi_poll+0x3c/0x158
[<00000000bb0c10eb>] net_rx_action+0xe8/0x210
[<000000003322eb9f>] __do_softirq+0x168/0x360
[<00000000d4037fcb>] irq_exit+0x9c/0xe8
[<00000000224da306>] plat_irq_dispatch+0x48/0xd0
[<00000000327ba56b>] handle_int+0x14c/0x158
[<000000003eae4681>] __r4k_wait+0x20/0x40
unreferenced object 0x800000000536a180 (size 216):
comm "softirq", pid 0, jiffies 4294964050 (age 221.140s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<0000000078af28d6>] kmem_cache_alloc+0x1ac/0x708
[<000000001d074ea2>] __build_skb+0x34/0xd8
[<00000000339b0f83>] __netdev_alloc_skb+0x118/0x1f0
[<00000000db3556b0>] cvm_oct_mem_fill_fpa+0x154/0x1a8
[<00000000a49e80de>] cvm_oct_napi_poll+0x4c0/0x988
[<00000000d0c3cba0>] __napi_poll+0x3c/0x158
[<00000000bb0c10eb>] net_rx_action+0xe8/0x210
[<000000003322eb9f>] __do_softirq+0x168/0x360
[<00000000d4037fcb>] irq_exit+0x9c/0xe8
[<00000000224da306>] plat_irq_dispatch+0x48/0xd0
[<00000000327ba56b>] handle_int+0x14c/0x158
[<000000003eae4681>] __r4k_wait+0x20/0x40
root@OpenWrt:~#
softirq is the SoC interrupt?
Edit: I've contacted the upstream maintainer and will see where it goes. But, this isn't a dnsmasq/adblock issue.