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    Subject[PATCH 1/1] task_work: Add local_irq_enable() into task_work_run()
    arch/alpha and probably some other architectures call
    do_notify_resume()->task_work_run() with irqs disabled.

    This wasn't noticed because key_replace_session_keyring() and
    then task_work_run() did spin_lock_irq() + spin_unlock_irq(),
    but this sequence was removed by 9da33de6.

    Add local_irq_enable() as a workaround, and WARN_ONCE() to
    catch other buggy callers.

    While at it, remove the unnecessary initialization and add
    smp_ to read_barrier_depends() in task_work_cancel().

    Reported-by: Thorsten Kranzkowski <dl8bcu@dl8bcu.de>
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    ---
    kernel/task_work.c | 8 ++++++--
    1 files changed, 6 insertions(+), 2 deletions(-)

    diff --git a/kernel/task_work.c b/kernel/task_work.c
    index 65bd3c9..d39190c 100644
    --- a/kernel/task_work.c
    +++ b/kernel/task_work.c
    @@ -25,7 +25,7 @@ struct callback_head *
    task_work_cancel(struct task_struct *task, task_work_func_t func)
    {
    struct callback_head **pprev = &task->task_works;
    - struct callback_head *work = NULL;
    + struct callback_head *work;
    unsigned long flags;
    /*
    * If cmpxchg() fails we continue without updating pprev.
    @@ -35,7 +35,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
    */
    raw_spin_lock_irqsave(&task->pi_lock, flags);
    while ((work = ACCESS_ONCE(*pprev))) {
    - read_barrier_depends();
    + smp_read_barrier_depends();
    if (work->func != func)
    pprev = &work->next;
    else if (cmpxchg(pprev, work, work->next) == work)
    @@ -51,6 +51,10 @@ void task_work_run(void)
    struct task_struct *task = current;
    struct callback_head *work, *head, *next;

    + if (WARN_ONCE(irqs_disabled(),
    + "do_notify_resume() with irqs disabled, fix this arch."))
    + local_irq_enable();
    +
    for (;;) {
    /*
    * work->func() can do task_work_add(), do not set
    --
    1.5.5.1



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