My bet would have been actually on aa283f49276e7d840a40fb01eee6de97eaa7e012
because it does some nasty things (enable interrupts in the middle
of __switch_to).
I looked through the old patchkit and couldn't find any specific
PREEMPT problems. All code it changes should run with preempt_off
You could verify with sticking WARN_ON_ONCE(preemptible()) into
all the places acc207616a91a413a50fdd8847a747c4a7324167
changes (__unlazy_fpu, math_state_restore) and see if that triggers
anywhere.
-Andi
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