Use of sti in entry.S question

From: Duncan Sands (baldrick@wanadoo.fr)
Date: Thu May 22 2003 - 02:39:13 EST

2.5/arch/i386/kernel/entry.S:

In work_resched, schedule may be called with
interrupts off:

work_resched:
        call schedule
        cli # make sure we don't miss an interrupt
                                        # setting need_resched or sigpending
                                        # between sampling and the iret
        movl TI_FLAGS(%ebp), %ecx
        andl $_TIF_WORK_MASK, %ecx # is there any work to be done other
                                        # than syscall tracing?
        jz restore_all
        testb $_TIF_NEED_RESCHED, %cl
        jnz work_resched <====== schedule with interrupts disabled

Is this a mistake or an optimization? Elsewhere in entry.S, interrupts
are turned on before calling schedule:

#ifdef CONFIG_PREEMPT
ENTRY(resume_kernel)
        cmpl $0,TI_PRE_COUNT(%ebp) # non-zero preempt_count ?
        jnz restore_all
need_resched:
        movl TI_FLAGS(%ebp), %ecx # need_resched set ?
        testb $_TIF_NEED_RESCHED, %cl
        jz restore_all
        testl $IF_MASK,EFLAGS(%esp) # interrupts off (exception path) ?
        jz restore_all
        movl $PREEMPT_ACTIVE,TI_PRE_COUNT(%ebp)
        sti <====== schedule with interrupts enabled
        call schedule
        movl $0,TI_PRE_COUNT(%ebp)
        cli
        jmp need_resched
#endif

Thanks,

Duncan.
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