Re: CONFIG_PREEMPT x86 assembly question

[Michal Schmidt]

Nikita V. Youshchenko wrote:
> In arch/i386/kernel/entry.S
>
> ...
> ENTRY(resume_kernel)
>  cmpl $0,TI_preempt_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_preempt_count(%ebp)
>  sti
>  call schedule
>  movl $0,TI_preempt_count(%ebp)
>  cli
>  jmp need_resched
> #endif
> ...
>
> Why, after return from schedule(), first 0 is written to 
> TI_preempt_count(%ebp), and only then interrupts are disabled?
> Wht not the reverse order?

It's already reversed in linux-2.6.10-rc2:
 ...
 call schedule
 cli
 movl $0,TI_preempt_count(%ebp)
 jmp need_resched

Michal
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