On 03/06, David Vrabel wrote: > > On 06/03/15 14:01, Oleg Nesterov wrote: > > > Not sure I understand it correctly after the first quick look, but > > > > 1. It conflicts with the recent changes in tip/x86/fpu > > > > 2. fpu_ini() initializes current->thread.fpu.state. This looks unneeded, > > the kernel threads no longer have FPU context and do not abuse CPU. > > > > 3. I can be easily wrong, but it looks buggy... Note that > > arch_dup_task_struct() doesn't allocate child->fpu.state if > > !tsk_used_math(parent). > > ...yes. It's bit-rotted a bit. > > > No, I do not think this patch is a good idea. Perhaps I am wrong, but I > > think we need other changes. And they should start from init_fpu(). > > But the general principle of avoiding the allocation in the #NM handler > and hence avoiding the need to re-enable IRQs is still a good idea, yes?
This needs more discussion, but in short so far I think that fpu_alloc() from #NM exception is fine if user_mode(regs) == T. Just do_device_not_available() should simply do conditional_sti(), I think. Perhaps it can even enable irqs unconditionally, but we need to verify that this is 100% correct. And I agree that "if (!tsk_used_math(tsk))" code in math_state_restore() should be removed. But not to avoid the allocation, and this needs other changes. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
