[Bug 255997] fpu_kern_thread is called before fpu_initialstate has been set in ktls_kern_thread

From: <bugzilla-noreply_at_freebsd.org>
Date: Thu, 27 May 2021 15:42:02 +0000
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255997

--- Comment #2 from Henning Zabel <h.zabel_at_beckhoff.com> ---
we are using a modified version of the freebsd kernel. because we do floating
point operations within spinlocks a "device not available" exception may break
these locks. because of this we avoid using fpu emulation for kernel threads
and restore a valid state in fpu_enter and fpu_kern_thread. we also restore the
fpu state within context switches to a kernel thread with FPU_KERN set. 

this modified kernel will not run, because ktls_kern_thread then tries to
restore an uninitialized state. thus, the ktls thread itself is not the
problem, but it the first hitting this situation.

currently it seems not to be a problem for the freebsd 13 kernel, nevertheless
its a fault.

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Received on Thu May 27 2021 - 15:42:02 UTC

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