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    Subject[PATCH 3/4] pids: fix fork_idle() to setup ->pids correctly
    copy_process(pid => &init_struct_pid) doesn't do attach_pid/etc.

    It shouldn't, but this means that the idle threads run with the wrong
    pids copied from the caller's task_struct. In x86 case the caller is
    either kernel_init() thread or keventd.

    In particular, this means that after the series of cpu_up/cpu_down an
    idle thread (which never exits) can run with .pid pointing to nowhere.

    Change fork_idle() to initialize idle->pids[] correctly. We only set
    .pid = &init_struct_pid but do not add .node to list, INIT_TASK() does
    the same for the boot-cpu idle thread (swapper).

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    ---

    kernel/fork.c | 14 +++++++++++++-
    1 file changed, 13 insertions(+), 1 deletion(-)

    --- 34-rc1/kernel/fork.c~3_FORK_IDLE_SET_PIDS 2010-03-24 18:07:03.000000000 +0100
    +++ 34-rc1/kernel/fork.c 2010-05-10 20:45:33.000000000 +0200
    @@ -1339,6 +1339,16 @@ noinline struct pt_regs * __cpuinit __at
    return regs;
    }

    +static inline void init_idle_pids(struct pid_link *links)
    +{
    + enum pid_type type;
    +
    + for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
    + INIT_HLIST_NODE(&links[type].node); /* not really needed */
    + links[type].pid = &init_struct_pid;
    + }
    +}
    +
    struct task_struct * __cpuinit fork_idle(int cpu)
    {
    struct task_struct *task;
    @@ -1346,8 +1356,10 @@ struct task_struct * __cpuinit fork_idle

    task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
    &init_struct_pid, 0);
    - if (!IS_ERR(task))
    + if (!IS_ERR(task)) {
    + init_idle_pids(task->pids);
    init_idle(task, cpu);
    + }

    return task;
    }


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