Messages in this thread | | | Date | Fri, 13 Mar 2015 15:55:42 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in flush_thread() |
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On 03/13, Borislav Petkov wrote: > > On Wed, Mar 11, 2015 at 06:35:07PM +0100, Oleg Nesterov wrote: > > drop_init_fpu() makes no sense. We need drop_fpu() and only if > > Oh, please explain why. I can try to rhyme it up as something like "we > don't need to restore FPU context when flushing the thread" but I'm not > sure...
Hmm. The changelog could be more clear. I'll send v2.
But please look at drop_init_fpu(). If eagerfpu == F it calls drop_fpu() and this is what we need. flush_thread() already has the "if (!use_eager_fpu())", we can shift drop_fpu() there.
Otherwise, if eagerfpu == T, drop_init_fpu() does restore_init_xstate() and this just burns CPU. Until flush_thread user_has_fpu/used_math this state restore_init_xstate() is pointless, this state will be lost after preemption.
> > + } else if (!used_math()) { > > /* kthread execs. TODO: cleanup this horror. */ > > if (WARN_ON(init_fpu(current))) > > force_sig(SIGKILL, current); > > Also, can we clean up the tsk/current usage here? > > We assign current to tsk and we work with it but then later use current > again. Needlessly confusing.
Agreed, will do.
Oleg.
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