Messages in this thread | | | Date | Mon, 8 Feb 2010 21:26:52 +0100 | From | Oleg Nesterov <> | Subject | Re: PATCH? process_32.c:__switch_to() calls __math_state_restore() before updating current_task |
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On 02/08, Suresh Siddha wrote: > > On Fri, 2010-02-05 at 04:44 -0800, Oleg Nesterov wrote: > > Could you please explain me another issue? I know nothing about fpu > > handling, I am reading this code trying to understand the unrelated > > bug with the old kernel. > > > > In short: why restore_i387_xstate() does init_fpu() when !used_math(), > > can't (or shouldn't) it merely do set_used_math() ? > > > > restore_i387_xstate: > > > > if (!used_math()) { > > err = init_fpu(tsk); > > if (err) > > return err; > > } > > > > note that buf != NULL. This means that used_math() was true when > > get_sigframe() was called, otherwise buf == sigcontext->fpstate > > would be NULL, right? > > No. When the signal is delivered sigcontext->fpstate can be null and > when we return from the signal handler, user can update the > sigcontext->fpstate pointer
Yes, I already realized this, see my next emails.
> and the user expects the kernel to update > the fpstate of the process accordingly.
but I didn't know it is "officially" allowed to populate .xstate this way.
Thanks Suresh for your explanations.
Oleg.
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