Floating point is forbidden in kernel code since the floating point
registers (and other floating point context) is not saved/restored
during system calls, for efficiency. I’m speculating here, but it
might be possible to manually save the floating point context while
doing some floating point operations. The problem arises if this code
is interrupted midway. Using a preemptive 2.6 kernel would easily
break here.

如果是這樣, 那就 Mask IRQ, 做完再 unmask 掉.  不知道可不可行.

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