diff options
Diffstat (limited to 'debian/patches-rt/futex-requeue-pi-fix.patch')
| -rw-r--r-- | debian/patches-rt/futex-requeue-pi-fix.patch | 113 |
1 files changed, 0 insertions, 113 deletions
diff --git a/debian/patches-rt/futex-requeue-pi-fix.patch b/debian/patches-rt/futex-requeue-pi-fix.patch deleted file mode 100644 index b7ab28303..000000000 --- a/debian/patches-rt/futex-requeue-pi-fix.patch +++ /dev/null @@ -1,113 +0,0 @@ -From: Steven Rostedt <rostedt@goodmis.org> -Date: Tue, 14 Jul 2015 14:26:34 +0200 -Subject: futex: Fix bug on when a requeued RT task times out -Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.10-rt7.tar.xz - -Requeue with timeout causes a bug with PREEMPT_RT_FULL. - -The bug comes from a timed out condition. - - - TASK 1 TASK 2 - ------ ------ - futex_wait_requeue_pi() - futex_wait_queue_me() - <timed out> - - double_lock_hb(); - - raw_spin_lock(pi_lock); - if (current->pi_blocked_on) { - } else { - current->pi_blocked_on = PI_WAKE_INPROGRESS; - run_spin_unlock(pi_lock); - spin_lock(hb->lock); <-- blocked! - - - plist_for_each_entry_safe(this) { - rt_mutex_start_proxy_lock(); - task_blocks_on_rt_mutex(); - BUG_ON(task->pi_blocked_on)!!!! - -The BUG_ON() actually has a check for PI_WAKE_INPROGRESS, but the -problem is that, after TASK 1 sets PI_WAKE_INPROGRESS, it then tries to -grab the hb->lock, which it fails to do so. As the hb->lock is a mutex, -it will block and set the "pi_blocked_on" to the hb->lock. - -When TASK 2 goes to requeue it, the check for PI_WAKE_INPROGESS fails -because the task1's pi_blocked_on is no longer set to that, but instead, -set to the hb->lock. - -The fix: - -When calling rt_mutex_start_proxy_lock() a check is made to see -if the proxy tasks pi_blocked_on is set. If so, exit out early. -Otherwise set it to a new flag PI_REQUEUE_INPROGRESS, which notifies -the proxy task that it is being requeued, and will handle things -appropriately. - - -Signed-off-by: Steven Rostedt <rostedt@goodmis.org> -Signed-off-by: Thomas Gleixner <tglx@linutronix.de> ---- - kernel/locking/rtmutex.c | 31 ++++++++++++++++++++++++++++++- - kernel/locking/rtmutex_common.h | 1 + - 2 files changed, 31 insertions(+), 1 deletion(-) - ---- a/kernel/locking/rtmutex.c -+++ b/kernel/locking/rtmutex.c -@@ -137,7 +137,8 @@ static void fixup_rt_mutex_waiters(struc - - static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter) - { -- return waiter && waiter != PI_WAKEUP_INPROGRESS; -+ return waiter && waiter != PI_WAKEUP_INPROGRESS && -+ waiter != PI_REQUEUE_INPROGRESS; - } - - /* -@@ -1784,6 +1785,34 @@ int __rt_mutex_start_proxy_lock(struct r - 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); ---- a/kernel/locking/rtmutex_common.h -+++ b/kernel/locking/rtmutex_common.h -@@ -131,6 +131,7 @@ 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, |