From: Sebastian Andrzej Siewior Date: Wed, 26 Jun 2019 17:44:18 +0200 Subject: [PATCH 272/353] Revert "futex: Fix bug on when a requeued RT task times out" Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=112b6c937ae5e417fe33cf5099310047a342e229 [ 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 Signed-off-by: Steven Rostedt (VMware) --- 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 ded2296f848a..a87b65447991 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; } /* @@ -2349,34 +2348,6 @@ 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 8e0c592273e6..627340e7427e 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,