Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

From: Suresh Siddha
Date: Sat Feb 01 2014 - 20:07:43 EST

On Sat, Feb 1, 2014 at 11:27 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> That said, regardless of the allocation issue, I do think that it's
> stupid for kernel_fpu_{begin,end} to save the math state if
> "used_math" was not set. So I do think__kernel_fpu_end() as-s is
> buggy and stupid.

For eager_fpu case, assumption was every task should always have
'used_math' set. But i think there is a race, where we drop the fpu
explicitly by doing drop_fpu() and meanwhile if we get an interrupt
etc that ends up using fpu?

so I will Ack for option "b", as option "a" breaks the features which
don't take into account cr0.TS.

Meanwhile I have the patch removing the delayed dynamic allocation for
non-eager fpu. will post it after some testing.

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