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    SubjectRe: [PATCH][BUG] Badness in smp_call_function at arch/i386/kernel/smp.c:552
    Zwane Mwaikambo <zwane@holomorphy.com> wrote:
    >
    > __handle_sysrq was modified to do a spin_lock_irqsave so we were
    > entering smp_send_stop with interrupts. So enable interrupts in
    > machine_shutdown().
    >
    > Signed-off-by: Zwane Mwaikambo <zwane@holomorphy.com>
    >
    > Index: linux-2.6.10-rc2-mm4/arch/i386/kernel/reboot.c
    > ===================================================================
    > RCS file: /home/cvsroot/linux-2.6.10-rc2-mm4/arch/i386/kernel/reboot.c,v
    > retrieving revision 1.1.1.1
    > diff -u -p -B -r1.1.1.1 reboot.c
    > --- linux-2.6.10-rc2-mm4/arch/i386/kernel/reboot.c 30 Nov 2004 18:52:19 -0000 1.1.1.1
    > +++ linux-2.6.10-rc2-mm4/arch/i386/kernel/reboot.c 3 Dec 2004 04:28:28 -0000
    > @@ -274,6 +274,8 @@ void machine_shutdown(void)
    > #ifdef CONFIG_SMP
    > int reboot_cpu_id;
    >
    > + local_irq_enable();

    Well, sort-of.

    If __handle_sysrq was really a normal IRQ handler then the correct thing to
    do here is to replace spin_lock_irqsave() with spin_lock(). But
    __handle_sysrq() can also be called via /proc/sysrq-trigger and via the
    handlers of multiple interrupt sources. So we're stuck with using
    spin_lock_irqsave().

    However enabling interrupts as you've done menas that theoretically we
    could deadlock on sysrq_key_table_lock if another sysrq happens at the
    wrong time.

    Which deadlock opportunity would you prefer? ;)
    -
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