Messages in this thread | | | Subject | Re: [PATCH 0/3] minor cleanups to EFLAGS initialisation in ret_from_fork | From | Peter Zijlstra <> | Date | Tue, 26 Jul 2011 16:46:34 +0200 |
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On Tue, 2011-07-26 at 01:47 +0400, Cyrill Gorcunov wrote: > > > 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... > > > > > > > This definitely doesn't look "obviously safe" to me. However, does > > anyone see a problem with unconditionally leaving IF disabled even on 32 > > bits (I haven't traced all the paths yet), i.e. doing the *opposite* of > > Ian's patch #2?
Right, enabling IRQs there isn't cool, currently there's still __ARCH_WANT_INTERRUPTS_ON_CTXSW but we're working hard on getting rid of that nightmare.
There's a number of very subtle things that can go wrong when you enable interrupts over the context switch.
Leaving IRQs disabled should be the right thing, on x86 we should _never_ have interrupts enabled there.
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