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