Messages in this thread | | | Date | Mon, 25 Jul 2011 22:20:50 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH 0/3] minor cleanups to EFLAGS initialisation in ret_from_fork |
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On Mon, Jul 25, 2011 at 02:19:02PM +0400, Cyrill Gorcunov wrote: > On Mon, Jul 25, 2011 at 10:58:03AM +0100, Ian Campbell wrote: > > The following series removes the use of a global kernel_eflags variable > > from the x86_64 ret_from_fork path and (very slightly) merges the 32 and > > 64 bit version of that code path. > > > > kernel_eflags could be made a __read_mostly but actually there is no > > reason to prefer the value at cpu_init() time to a compile time constant > > value for the initial eflags after a fork. > > > > Ian. > > > > Thanks, Ian! I think noone against this simplification, Peter, Andi? > > Cyrill
Ian, I've missed in first place that you've opened IRQs window _before_ schedule_tail() call, ie it's not 1:1 code mapping as it was before.
Note kernel_eflags has IF clear and what we have: the ret_from_fork on x86-64 happens _only_ inside context_switch call, ie
schedule (sched.c) ... raw_spin_lock_irq ... context_switch switch_to "jnz ret_from_fork\n\t" pushq_cfi kernel_eflags(%rip) popfq_cfi # reset kernel eflags
---> irqs are still disabled
call schedule_tail # rdi: 'prev' task parameter finish_lock_switch raw_spin_unlock_irq
I bet raw_spin_lock_irq at the beginning of the schedule() is set for a reason and such change is not safe. Though I may be missing something again...
Cyrill
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