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    SubjectRe: [PATCH] irq: Fix race condition when stopping the irq thread
    On Thu, 1 Dec 2011, Ido Yariv wrote:

    > In irq_wait_for_interrupt(), the should_stop member is verified before
    > setting the task's state to TASK_INTERRUPTIBLE and calling schedule().
    > In case kthread_stop sets should_stop and wakes up the process after
    > should_stop is checked by the irq thread but before the task's state is
    > changed, the irq thread might never exit:
    >
    > kthread_stop irq_wait_for_interrupt
    > ------------ ----------------------
    >
    > ...
    > ... while (!kthread_should_stop()) {
    > kthread->should_stop = 1;
    > wake_up_process(k);
    > wait_for_completion(&kthread->exited);
    > ...
    > set_current_state(TASK_INTERRUPTIBLE);
    >
    > ...
    >
    > schedule();
    > }
    > ...
    >
    > Fix this by checking if the thread should stop after modifying the
    > task's state.

    Good catch! I restructure it to:

    --- tip.orig/kernel/irq/manage.c
    +++ tip/kernel/irq/manage.c
    @@ -623,8 +623,9 @@ static irqreturn_t irq_nested_primary_ha

    static int irq_wait_for_interrupt(struct irqaction *action)
    {
    + set_current_state(TASK_INTERRUPTIBLE);
    +
    while (!kthread_should_stop()) {
    - set_current_state(TASK_INTERRUPTIBLE);

    if (test_and_clear_bit(IRQTF_RUNTHREAD,
    &action->thread_flags)) {
    @@ -632,7 +633,9 @@ static int irq_wait_for_interrupt(struct
    return 0;
    }
    schedule();
    + set_current_state(TASK_INTERRUPTIBLE);
    }
    + __set_current_state(TASK_RUNNING);
    return -1;
    }

    That saves us the extra conditional in the loop.
    Thanks,

    tglx


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