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-rw-r--r--debian/patches-rt/0129-rtmutex-Handle-the-various-new-futex-race-conditions.patch254
1 files changed, 254 insertions, 0 deletions
diff --git a/debian/patches-rt/0129-rtmutex-Handle-the-various-new-futex-race-conditions.patch b/debian/patches-rt/0129-rtmutex-Handle-the-various-new-futex-race-conditions.patch
new file mode 100644
index 000000000..bdf75c3c6
--- /dev/null
+++ b/debian/patches-rt/0129-rtmutex-Handle-the-various-new-futex-race-conditions.patch
@@ -0,0 +1,254 @@
+From 9c83cf8ce7911f4f00f4fc71b365a30ebed5fdf4 Mon Sep 17 00:00:00 2001
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Fri, 10 Jun 2011 11:04:15 +0200
+Subject: [PATCH 129/347] rtmutex: Handle the various new futex race conditions
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz
+
+RT opens a few new interesting race conditions in the rtmutex/futex
+combo due to futex hash bucket lock being a 'sleeping' spinlock and
+therefor not disabling preemption.
+
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+---
+ kernel/futex.c | 77 ++++++++++++++++++++++++++-------
+ kernel/locking/rtmutex.c | 36 ++++++++++++---
+ kernel/locking/rtmutex_common.h | 2 +
+ 3 files changed, 94 insertions(+), 21 deletions(-)
+
+diff --git a/kernel/futex.c b/kernel/futex.c
+index ac015d1dd16c..dc2d81d11b17 100644
+--- a/kernel/futex.c
++++ b/kernel/futex.c
+@@ -2253,6 +2253,16 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+ requeue_pi_wake_futex(this, &key2, hb2);
+ drop_count++;
+ continue;
++ } else if (ret == -EAGAIN) {
++ /*
++ * Waiter was woken by timeout or
++ * signal and has set pi_blocked_on to
++ * PI_WAKEUP_INPROGRESS before we
++ * tried to enqueue it on the rtmutex.
++ */
++ this->pi_state = NULL;
++ put_pi_state(pi_state);
++ continue;
+ } else if (ret) {
+ /*
+ * rt_mutex_start_proxy_lock() detected a
+@@ -3331,7 +3341,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+ {
+ struct hrtimer_sleeper timeout, *to = NULL;
+ struct rt_mutex_waiter rt_waiter;
+- struct futex_hash_bucket *hb;
++ struct futex_hash_bucket *hb, *hb2;
+ union futex_key key2 = FUTEX_KEY_INIT;
+ struct futex_q q = futex_q_init;
+ int res, ret;
+@@ -3389,20 +3399,55 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+ /* Queue the futex_q, drop the hb lock, wait for wakeup. */
+ futex_wait_queue_me(hb, &q, to);
+
+- spin_lock(&hb->lock);
+- ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
+- spin_unlock(&hb->lock);
+- if (ret)
+- goto out_put_keys;
++ /*
++ * On RT we must avoid races with requeue and trying to block
++ * on two mutexes (hb->lock and uaddr2's rtmutex) by
++ * serializing access to pi_blocked_on with pi_lock.
++ */
++ raw_spin_lock_irq(&current->pi_lock);
++ if (current->pi_blocked_on) {
++ /*
++ * We have been requeued or are in the process of
++ * being requeued.
++ */
++ raw_spin_unlock_irq(&current->pi_lock);
++ } else {
++ /*
++ * Setting pi_blocked_on to PI_WAKEUP_INPROGRESS
++ * prevents a concurrent requeue from moving us to the
++ * uaddr2 rtmutex. After that we can safely acquire
++ * (and possibly block on) hb->lock.
++ */
++ current->pi_blocked_on = PI_WAKEUP_INPROGRESS;
++ raw_spin_unlock_irq(&current->pi_lock);
++
++ spin_lock(&hb->lock);
++
++ /*
++ * Clean up pi_blocked_on. We might leak it otherwise
++ * when we succeeded with the hb->lock in the fast
++ * path.
++ */
++ raw_spin_lock_irq(&current->pi_lock);
++ current->pi_blocked_on = NULL;
++ raw_spin_unlock_irq(&current->pi_lock);
++
++ ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
++ spin_unlock(&hb->lock);
++ if (ret)
++ goto out_put_keys;
++ }
+
+ /*
+- * In order for us to be here, we know our q.key == key2, and since
+- * we took the hb->lock above, we also know that futex_requeue() has
+- * completed and we no longer have to concern ourselves with a wakeup
+- * race with the atomic proxy lock acquisition by the requeue code. The
+- * futex_requeue dropped our key1 reference and incremented our key2
+- * reference count.
++ * In order to be here, we have either been requeued, are in
++ * the process of being requeued, or requeue successfully
++ * acquired uaddr2 on our behalf. If pi_blocked_on was
++ * non-null above, we may be racing with a requeue. Do not
++ * rely on q->lock_ptr to be hb2->lock until after blocking on
++ * hb->lock or hb2->lock. The futex_requeue dropped our key1
++ * reference and incremented our key2 reference count.
+ */
++ hb2 = hash_futex(&key2);
+
+ /* Check if the requeue code acquired the second futex for us. */
+ if (!q.rt_waiter) {
+@@ -3411,14 +3456,15 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+ * did a lock-steal - fix up the PI-state in that case.
+ */
+ if (q.pi_state && (q.pi_state->owner != current)) {
+- spin_lock(q.lock_ptr);
++ spin_lock(&hb2->lock);
++ BUG_ON(&hb2->lock != q.lock_ptr);
+ ret = fixup_pi_state_owner(uaddr2, &q, current);
+ /*
+ * Drop the reference to the pi state which
+ * the requeue_pi() code acquired for us.
+ */
+ put_pi_state(q.pi_state);
+- spin_unlock(q.lock_ptr);
++ spin_unlock(&hb2->lock);
+ /*
+ * Adjust the return value. It's either -EFAULT or
+ * success (1) but the caller expects 0 for success.
+@@ -3437,7 +3483,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+ pi_mutex = &q.pi_state->pi_mutex;
+ ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
+
+- spin_lock(q.lock_ptr);
++ spin_lock(&hb2->lock);
++ BUG_ON(&hb2->lock != q.lock_ptr);
+ if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
+ ret = 0;
+
+diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
+index 4bec24dfafc6..9d472eb48ba7 100644
+--- a/kernel/locking/rtmutex.c
++++ b/kernel/locking/rtmutex.c
+@@ -135,6 +135,11 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
+ WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
+ }
+
++static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter)
++{
++ return waiter && waiter != PI_WAKEUP_INPROGRESS;
++}
++
+ /*
+ * We can speed up the acquire/release, if there's no debugging state to be
+ * set up.
+@@ -379,7 +384,8 @@ int max_lock_depth = 1024;
+
+ static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
+ {
+- return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
++ return rt_mutex_real_waiter(p->pi_blocked_on) ?
++ p->pi_blocked_on->lock : NULL;
+ }
+
+ /*
+@@ -515,7 +521,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
+ * reached or the state of the chain has changed while we
+ * dropped the locks.
+ */
+- if (!waiter)
++ if (!rt_mutex_real_waiter(waiter))
+ goto out_unlock_pi;
+
+ /*
+@@ -951,6 +957,22 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
+ return -EDEADLK;
+
+ raw_spin_lock(&task->pi_lock);
++ /*
++ * In the case of futex requeue PI, this will be a proxy
++ * lock. The task will wake unaware that it is enqueueed on
++ * this lock. Avoid blocking on two locks and corrupting
++ * pi_blocked_on via the PI_WAKEUP_INPROGRESS
++ * flag. futex_wait_requeue_pi() sets this when it wakes up
++ * before requeue (due to a signal or timeout). Do not enqueue
++ * the task if PI_WAKEUP_INPROGRESS is set.
++ */
++ if (task != current && task->pi_blocked_on == PI_WAKEUP_INPROGRESS) {
++ raw_spin_unlock(&task->pi_lock);
++ return -EAGAIN;
++ }
++
++ BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));
++
+ waiter->task = task;
+ waiter->lock = lock;
+ waiter->prio = task->prio;
+@@ -974,7 +996,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
+ rt_mutex_enqueue_pi(owner, waiter);
+
+ rt_mutex_adjust_prio(owner);
+- if (owner->pi_blocked_on)
++ if (rt_mutex_real_waiter(owner->pi_blocked_on))
+ chain_walk = 1;
+ } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
+ chain_walk = 1;
+@@ -1070,7 +1092,7 @@ static void remove_waiter(struct rt_mutex *lock,
+ {
+ bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
+ struct task_struct *owner = rt_mutex_owner(lock);
+- struct rt_mutex *next_lock;
++ struct rt_mutex *next_lock = NULL;
+
+ lockdep_assert_held(&lock->wait_lock);
+
+@@ -1096,7 +1118,8 @@ static void remove_waiter(struct rt_mutex *lock,
+ rt_mutex_adjust_prio(owner);
+
+ /* Store the lock on which owner is blocked or NULL */
+- next_lock = task_blocked_on_lock(owner);
++ if (rt_mutex_real_waiter(owner->pi_blocked_on))
++ next_lock = task_blocked_on_lock(owner);
+
+ raw_spin_unlock(&owner->pi_lock);
+
+@@ -1132,7 +1155,8 @@ void rt_mutex_adjust_pi(struct task_struct *task)
+ raw_spin_lock_irqsave(&task->pi_lock, flags);
+
+ waiter = task->pi_blocked_on;
+- if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
++ if (!rt_mutex_real_waiter(waiter) ||
++ rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ return;
+ }
+diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
+index ca6fb489007b..8f39bc139735 100644
+--- a/kernel/locking/rtmutex_common.h
++++ b/kernel/locking/rtmutex_common.h
+@@ -130,6 +130,8 @@ enum rtmutex_chainwalk {
+ /*
+ * PI-futex support (proxy locking functions, etc.):
+ */
++#define PI_WAKEUP_INPROGRESS ((struct rt_mutex_waiter *) 1)
++
+ extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
+ extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
+ struct task_struct *proxy_owner);
+--
+2.36.1
+
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