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    Subject[patch 29/32] softirq: remove BUG_ONs which can incorrectly trigger
    -stable review patch.  If anyone has any objections, please let us know.

    From: Zachary Amsden <>

    It is possible to have tasklets get scheduled before softirqd has had a chance
    to spawn on all CPUs. This is totally harmless; after success during action
    CPU_UP_PREPARE, action CPU_ONLINE will be called, which immediately wakes
    softirqd on the appropriate CPU to process the already pending tasklets. So
    there is no danger of having a missed wakeup for any tasklets that were
    already pending.

    In particular, i386 is affected by this during startup, and is visible when
    using a very large initrd; during the time it takes for the initrd to be
    decompressed, a timer IRQ can come in and schedule RCU callbacks. It is also
    possible that resending of a hardware IRQ via a softirq triggers the same bug.

    Because of different timing conditions, this shows up in all emulators and
    virtual machines tested, including Xen, VMware, Virtual PC, and Qemu. It is
    also possible to trigger on native hardware with a large enough initrd,
    although I don't have a reliable case demonstrating that.

    Signed-off-by: Zachary Amsden <>
    Cc: <>
    Cc: Ingo Molnar <>
    Cc: <>
    Signed-off-by: Andrew Morton <>
    Signed-off-by: Chris Wright <>

    kernel/softirq.c | 2 --
    1 file changed, 2 deletions(-)

    --- linux-2.6.19.orig/kernel/softirq.c
    +++ linux-2.6.19/kernel/softirq.c
    @@ -574,8 +574,6 @@ static int __cpuinit cpu_callback(struct

    switch (action) {
    case CPU_UP_PREPARE:
    - BUG_ON(per_cpu(tasklet_vec, hotcpu).list);
    - BUG_ON(per_cpu(tasklet_hi_vec, hotcpu).list);
    p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
    if (IS_ERR(p)) {
    printk("ksoftirqd for %i failed\n", hotcpu);
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