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Devin WittmayerandFelix Fietkau
5d68813ec0
mt7921_config() holds dev->mutex across ieee80211_iterate_active_interfaces(), which takes local->iflist_mtx. mac80211 uses the opposite order: ieee80211_del_virtual_monitor() holds iflist_mtx while calling drv_unassign_vif_chanctx(), and mt792x_unassign_vif_chanctx() takes dev->mutex. Deleting a monitor interface that has a channel assigned reaches the second order and lockdep reports the cycle. The driver side of it: -> #1 (&local->iflist_mtx){+.+.}-{4:4}: __mutex_lock+0xda/0x1070 ieee80211_iterate_interfaces+0x34/0x70 [mac80211] mt7921_config+0xb8/0xe0 [mt7921_common] drv_config+0x63/0x1d0 [mac80211] .config is only reached through drv_config(), which asserts the wiphy mutex, so ieee80211_iterate_active_interfaces_mtx() can be used. It walks the same list under the wiphy mutex and never takes iflist_mtx, which drops the driver's dev->mutex -> iflist_mtx edge. Fixes: cbaa0a404f8d ("mt76: mt7921: fix up the monitor mode") Link: https://lore.kernel.org/linux-wireless/[email protected]/ Signed-off-by: Devin Wittmayer <[email protected]> Link: https://patch.msgid.link/[email protected] Signed-off-by: Felix Fietkau <[email protected]>