Re: x86-64 preemption fix from IRQ and BKL in 2.6.12-rc1-mm2

[Andi Kleen <ak@muc.de>]

On Fri, Mar 25, 2005 at 08:26:25PM +0100, Christophe Saout wrote:
> Fortunately the kernel locked up and there was no data corruption.
> 
> I've got PREEMPT and PREEMPT_BKL enabled under UP.
> 
> I just took a look at the change and found this:
> 
> x86-64 does this (in entry.S):
> 
>         bt   $9,EFLAGS-ARGOFFSET(%rsp)  /* interrupts off? */
>         jnc   retint_restore_args
>         movl $PREEMPT_ACTIVE,threadinfo_preempt_count(%rcx)
>         sti
>         call schedule
>         cli
>         GET_THREAD_INFO(%rcx)
>         movl $0,threadinfo_preempt_count(%rcx)
>         jmp exit_intr
> 
> while i386 does this:
> 
>         testl $IF_MASK,EFLAGS(%esp)     # interrupts off (exception path) ?
>         jz restore_all
>         call preempt_schedule_irq
>         jmp need_resched
> 
> preempt_schedule_irq is not an i386 specific function and seems to take
> special care of BKL preemption and since reiserfs does use the BKL to do
> certain things I think this actually might be the problem...?

Hmm, preempt_schedule_irq is not in mainline as far as I can see.
My patches are always for mainline; i dont do a special
patch kit for -mm*

It looks like a unfortunate interaction with some other patches
in mm. Andrew, can you disable CONFIG_PREEMPT on x86-64 in
mm for now?

Just calling preempt_schedule_irq may also work, 
but most likely the patch that introduces that function needs
careful reading if it does not require more support from architectures.
BTW I suspect it will break other archs too...

> Unfortunately I don't have a amd64 machine to play with, so can somebody
> please check this?

How did you generate the crash dumps above then?

-Andi
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