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    Subject[PATCH RT 10/16] Revert "futex: Fix bug on when a requeued RT task times out"
    4.19.59-rt24-rc1 stable review patch.
    If anyone has any objections, please let me know.

    ------------------

    From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

    [ Upstream commit f1a170cb3289a48df26cae3c60d77608f7a988bb ]

    Drop the RT fixup, the futex code will be changed to avoid the need for
    the workaround.

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    ---
    kernel/locking/rtmutex.c | 31 +------------------------------
    kernel/locking/rtmutex_common.h | 1 -
    2 files changed, 1 insertion(+), 31 deletions(-)

    diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
    index 2a9bf2443acc..7f6f402e04ae 100644
    --- a/kernel/locking/rtmutex.c
    +++ b/kernel/locking/rtmutex.c
    @@ -144,8 +144,7 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)

    static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter)
    {
    - return waiter && waiter != PI_WAKEUP_INPROGRESS &&
    - waiter != PI_REQUEUE_INPROGRESS;
    + return waiter && waiter != PI_WAKEUP_INPROGRESS;
    }

    /*
    @@ -2350,34 +2349,6 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
    if (try_to_take_rt_mutex(lock, task, NULL))
    return 1;

    -#ifdef CONFIG_PREEMPT_RT_FULL
    - /*
    - * In PREEMPT_RT there's an added race.
    - * If the task, that we are about to requeue, times out,
    - * it can set the PI_WAKEUP_INPROGRESS. This tells the requeue
    - * to skip this task. But right after the task sets
    - * its pi_blocked_on to PI_WAKEUP_INPROGRESS it can then
    - * block on the spin_lock(&hb->lock), which in RT is an rtmutex.
    - * This will replace the PI_WAKEUP_INPROGRESS with the actual
    - * lock that it blocks on. We *must not* place this task
    - * on this proxy lock in that case.
    - *
    - * To prevent this race, we first take the task's pi_lock
    - * and check if it has updated its pi_blocked_on. If it has,
    - * we assume that it woke up and we return -EAGAIN.
    - * Otherwise, we set the task's pi_blocked_on to
    - * PI_REQUEUE_INPROGRESS, so that if the task is waking up
    - * it will know that we are in the process of requeuing it.
    - */
    - raw_spin_lock(&task->pi_lock);
    - if (task->pi_blocked_on) {
    - raw_spin_unlock(&task->pi_lock);
    - return -EAGAIN;
    - }
    - task->pi_blocked_on = PI_REQUEUE_INPROGRESS;
    - raw_spin_unlock(&task->pi_lock);
    -#endif
    -
    /* We enforce deadlock detection for futexes */
    ret = task_blocks_on_rt_mutex(lock, waiter, task,
    RT_MUTEX_FULL_CHAINWALK);
    diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
    index 546aaf058b9e..a501f3b47081 100644
    --- a/kernel/locking/rtmutex_common.h
    +++ b/kernel/locking/rtmutex_common.h
    @@ -133,7 +133,6 @@ enum rtmutex_chainwalk {
    * PI-futex support (proxy locking functions, etc.):
    */
    #define PI_WAKEUP_INPROGRESS ((struct rt_mutex_waiter *) 1)
    -#define PI_REQUEUE_INPROGRESS ((struct rt_mutex_waiter *) 2)

    extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
    extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
    --
    2.20.1

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