The MT7531 on the Flint 2 is MDIO-attached and shares the SoC MDIO bus
with the 2.5G WAN PHY. On 6.18.49 mt7530_get_stats64 takes the MDIO
mutex under the RCU read lock that /proc/net/dev readers hold; when the
WAN PHY is renegotiating (PPPoE flap) the mutex is contended, the read
sleeps in atomic context and the box oopses:
BUG: scheduling while atomic: zerotier-one/1748/0x00000002
mt7530_get_stats64 -> dsa_user_get_stats64 -> dev_seq_show
Unable to handle kernel paging request at 0000afa547cef5f0
Vendor upstream 07d99587396024932e02474c3a5bede71d108454 (mainline
2026-05-04, absent from linux-6.18.y). Applies to v6.18.49 with one
fuzz-1 hunk (6.18 still exports mt7530_switch_ops).
Storage=volatile left nothing behind for the 2026-09-23/24 reboots: the
last persisted entry is journald stopping during the 2026-09-22 switch,
and /sys/fs/pstore is empty too. Keep the eMMC-wear intent with a 256M
cap and a 1 min sync interval matching the ext4 commit=60.
kurogeek