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-rw-r--r--debian/patches-rt/0302-futex-Make-the-futex_hash_bucket-spinlock_t-again-an.patch731
1 files changed, 731 insertions, 0 deletions
diff --git a/debian/patches-rt/0302-futex-Make-the-futex_hash_bucket-spinlock_t-again-an.patch b/debian/patches-rt/0302-futex-Make-the-futex_hash_bucket-spinlock_t-again-an.patch
new file mode 100644
index 000000000..224b6a81a
--- /dev/null
+++ b/debian/patches-rt/0302-futex-Make-the-futex_hash_bucket-spinlock_t-again-an.patch
@@ -0,0 +1,731 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Mon, 7 Oct 2019 16:45:18 +0200
+Subject: [PATCH 302/342] futex: Make the futex_hash_bucket spinlock_t again
+ and bring back its old state
+Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=db07179f5403257fab1645f3d1b5016389d2d3bb
+
+[ Upstream commit 954ad80c23edfe71f4e8ce70b961eac884320c3a ]
+
+This is an all-in-one patch that reverts the patches:
+ futex: Make the futex_hash_bucket lock raw
+ futex: Delay deallocation of pi_state
+
+and adds back the old patches we had:
+ futex: workaround migrate_disable/enable in different context
+ rtmutex: Handle the various new futex race conditions
+ futex: Fix bug on when a requeued RT task times out
+ futex: Ensure lock/unlock symetry versus pi_lock and hash bucket lock
+
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
+---
+ kernel/futex.c | 228 ++++++++++++++++++--------------
+ kernel/locking/rtmutex.c | 65 ++++++++-
+ kernel/locking/rtmutex_common.h | 3 +
+ 3 files changed, 193 insertions(+), 103 deletions(-)
+
+diff --git a/kernel/futex.c b/kernel/futex.c
+index 2fc6bedb460e..81090f7a3ed9 100644
+--- a/kernel/futex.c
++++ b/kernel/futex.c
+@@ -243,7 +243,7 @@ struct futex_q {
+ struct plist_node list;
+
+ struct task_struct *task;
+- raw_spinlock_t *lock_ptr;
++ spinlock_t *lock_ptr;
+ union futex_key key;
+ struct futex_pi_state *pi_state;
+ struct rt_mutex_waiter *rt_waiter;
+@@ -264,7 +264,7 @@ static const struct futex_q futex_q_init = {
+ */
+ struct futex_hash_bucket {
+ atomic_t waiters;
+- raw_spinlock_t lock;
++ spinlock_t lock;
+ struct plist_head chain;
+ } ____cacheline_aligned_in_smp;
+
+@@ -871,13 +871,13 @@ static void get_pi_state(struct futex_pi_state *pi_state)
+ * Drops a reference to the pi_state object and frees or caches it
+ * when the last reference is gone.
+ */
+-static struct futex_pi_state *__put_pi_state(struct futex_pi_state *pi_state)
++static void put_pi_state(struct futex_pi_state *pi_state)
+ {
+ if (!pi_state)
+- return NULL;
++ return;
+
+ if (!atomic_dec_and_test(&pi_state->refcount))
+- return NULL;
++ return;
+
+ /*
+ * If pi_state->owner is NULL, the owner is most probably dying
+@@ -892,7 +892,9 @@ static struct futex_pi_state *__put_pi_state(struct futex_pi_state *pi_state)
+ raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
+ }
+
+- if (!current->pi_state_cache) {
++ if (current->pi_state_cache) {
++ kfree(pi_state);
++ } else {
+ /*
+ * pi_state->list is already empty.
+ * clear pi_state->owner.
+@@ -901,30 +903,6 @@ static struct futex_pi_state *__put_pi_state(struct futex_pi_state *pi_state)
+ pi_state->owner = NULL;
+ atomic_set(&pi_state->refcount, 1);
+ current->pi_state_cache = pi_state;
+- pi_state = NULL;
+- }
+- return pi_state;
+-}
+-
+-static void put_pi_state(struct futex_pi_state *pi_state)
+-{
+- kfree(__put_pi_state(pi_state));
+-}
+-
+-static void put_pi_state_atomic(struct futex_pi_state *pi_state,
+- struct list_head *to_free)
+-{
+- if (__put_pi_state(pi_state))
+- list_add(&pi_state->list, to_free);
+-}
+-
+-static void free_pi_state_list(struct list_head *to_free)
+-{
+- struct futex_pi_state *p, *next;
+-
+- list_for_each_entry_safe(p, next, to_free, list) {
+- list_del(&p->list);
+- kfree(p);
+ }
+ }
+
+@@ -941,7 +919,6 @@ static void exit_pi_state_list(struct task_struct *curr)
+ struct futex_pi_state *pi_state;
+ struct futex_hash_bucket *hb;
+ union futex_key key = FUTEX_KEY_INIT;
+- LIST_HEAD(to_free);
+
+ if (!futex_cmpxchg_enabled)
+ return;
+@@ -975,7 +952,7 @@ static void exit_pi_state_list(struct task_struct *curr)
+ }
+ raw_spin_unlock_irq(&curr->pi_lock);
+
+- raw_spin_lock(&hb->lock);
++ spin_lock(&hb->lock);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ raw_spin_lock(&curr->pi_lock);
+ /*
+@@ -985,8 +962,10 @@ static void exit_pi_state_list(struct task_struct *curr)
+ if (head->next != next) {
+ /* retain curr->pi_lock for the loop invariant */
+ raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
+- raw_spin_unlock(&hb->lock);
+- put_pi_state_atomic(pi_state, &to_free);
++ raw_spin_unlock_irq(&curr->pi_lock);
++ spin_unlock(&hb->lock);
++ raw_spin_lock_irq(&curr->pi_lock);
++ put_pi_state(pi_state);
+ continue;
+ }
+
+@@ -997,7 +976,7 @@ static void exit_pi_state_list(struct task_struct *curr)
+
+ raw_spin_unlock(&curr->pi_lock);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+- raw_spin_unlock(&hb->lock);
++ spin_unlock(&hb->lock);
+
+ rt_mutex_futex_unlock(&pi_state->pi_mutex);
+ put_pi_state(pi_state);
+@@ -1005,8 +984,6 @@ static void exit_pi_state_list(struct task_struct *curr)
+ raw_spin_lock_irq(&curr->pi_lock);
+ }
+ raw_spin_unlock_irq(&curr->pi_lock);
+-
+- free_pi_state_list(&to_free);
+ }
+ #else
+ static inline void exit_pi_state_list(struct task_struct *curr) { }
+@@ -1548,7 +1525,7 @@ static void __unqueue_futex(struct futex_q *q)
+ {
+ struct futex_hash_bucket *hb;
+
+- if (WARN_ON_SMP(!q->lock_ptr || !raw_spin_is_locked(q->lock_ptr))
++ if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
+ || WARN_ON(plist_node_empty(&q->list)))
+ return;
+
+@@ -1668,21 +1645,21 @@ static inline void
+ double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+ {
+ if (hb1 <= hb2) {
+- raw_spin_lock(&hb1->lock);
++ spin_lock(&hb1->lock);
+ if (hb1 < hb2)
+- raw_spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
++ spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
+ } else { /* hb1 > hb2 */
+- raw_spin_lock(&hb2->lock);
+- raw_spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
++ spin_lock(&hb2->lock);
++ spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
+ }
+ }
+
+ static inline void
+ double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+ {
+- raw_spin_unlock(&hb1->lock);
++ spin_unlock(&hb1->lock);
+ if (hb1 != hb2)
+- raw_spin_unlock(&hb2->lock);
++ spin_unlock(&hb2->lock);
+ }
+
+ /*
+@@ -1710,7 +1687,7 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
+ if (!hb_waiters_pending(hb))
+ goto out_put_key;
+
+- raw_spin_lock(&hb->lock);
++ spin_lock(&hb->lock);
+
+ plist_for_each_entry_safe(this, next, &hb->chain, list) {
+ if (match_futex (&this->key, &key)) {
+@@ -1729,7 +1706,7 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
+ }
+ }
+
+- raw_spin_unlock(&hb->lock);
++ spin_unlock(&hb->lock);
+ wake_up_q(&wake_q);
+ out_put_key:
+ put_futex_key(&key);
+@@ -2042,7 +2019,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+ struct futex_hash_bucket *hb1, *hb2;
+ struct futex_q *this, *next;
+ DEFINE_WAKE_Q(wake_q);
+- LIST_HEAD(to_free);
+
+ if (nr_wake < 0 || nr_requeue < 0)
+ return -EINVAL;
+@@ -2281,6 +2257,16 @@ 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
+@@ -2291,7 +2277,7 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+ * object.
+ */
+ this->pi_state = NULL;
+- put_pi_state_atomic(pi_state, &to_free);
++ put_pi_state(pi_state);
+ /*
+ * We stop queueing more waiters and let user
+ * space deal with the mess.
+@@ -2308,7 +2294,7 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+ * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
+ * need to drop it here again.
+ */
+- put_pi_state_atomic(pi_state, &to_free);
++ put_pi_state(pi_state);
+
+ out_unlock:
+ double_unlock_hb(hb1, hb2);
+@@ -2329,7 +2315,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+ out_put_key1:
+ put_futex_key(&key1);
+ out:
+- free_pi_state_list(&to_free);
+ return ret ? ret : task_count;
+ }
+
+@@ -2353,7 +2338,7 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
+
+ q->lock_ptr = &hb->lock;
+
+- raw_spin_lock(&hb->lock); /* implies smp_mb(); (A) */
++ spin_lock(&hb->lock); /* implies smp_mb(); (A) */
+ return hb;
+ }
+
+@@ -2361,7 +2346,7 @@ static inline void
+ queue_unlock(struct futex_hash_bucket *hb)
+ __releases(&hb->lock)
+ {
+- raw_spin_unlock(&hb->lock);
++ spin_unlock(&hb->lock);
+ hb_waiters_dec(hb);
+ }
+
+@@ -2400,7 +2385,7 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+ __releases(&hb->lock)
+ {
+ __queue_me(q, hb);
+- raw_spin_unlock(&hb->lock);
++ spin_unlock(&hb->lock);
+ }
+
+ /**
+@@ -2416,41 +2401,41 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+ */
+ static int unqueue_me(struct futex_q *q)
+ {
+- raw_spinlock_t *lock_ptr;
++ spinlock_t *lock_ptr;
+ int ret = 0;
+
+ /* In the common case we don't take the spinlock, which is nice. */
+ retry:
+ /*
+- * q->lock_ptr can change between this read and the following
+- * raw_spin_lock. Use READ_ONCE to forbid the compiler from reloading
+- * q->lock_ptr and optimizing lock_ptr out of the logic below.
++ * q->lock_ptr can change between this read and the following spin_lock.
++ * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
++ * optimizing lock_ptr out of the logic below.
+ */
+ lock_ptr = READ_ONCE(q->lock_ptr);
+ if (lock_ptr != NULL) {
+- raw_spin_lock(lock_ptr);
++ spin_lock(lock_ptr);
+ /*
+ * q->lock_ptr can change between reading it and
+- * raw_spin_lock(), causing us to take the wrong lock. This
++ * spin_lock(), causing us to take the wrong lock. This
+ * corrects the race condition.
+ *
+ * Reasoning goes like this: if we have the wrong lock,
+ * q->lock_ptr must have changed (maybe several times)
+- * between reading it and the raw_spin_lock(). It can
+- * change again after the raw_spin_lock() but only if it was
+- * already changed before the raw_spin_lock(). It cannot,
++ * between reading it and the spin_lock(). It can
++ * change again after the spin_lock() but only if it was
++ * already changed before the spin_lock(). It cannot,
+ * however, change back to the original value. Therefore
+ * we can detect whether we acquired the correct lock.
+ */
+ if (unlikely(lock_ptr != q->lock_ptr)) {
+- raw_spin_unlock(lock_ptr);
++ spin_unlock(lock_ptr);
+ goto retry;
+ }
+ __unqueue_futex(q);
+
+ BUG_ON(q->pi_state);
+
+- raw_spin_unlock(lock_ptr);
++ spin_unlock(lock_ptr);
+ ret = 1;
+ }
+
+@@ -2466,16 +2451,13 @@ static int unqueue_me(struct futex_q *q)
+ static void unqueue_me_pi(struct futex_q *q)
+ __releases(q->lock_ptr)
+ {
+- struct futex_pi_state *ps;
+-
+ __unqueue_futex(q);
+
+ BUG_ON(!q->pi_state);
+- ps = __put_pi_state(q->pi_state);
++ put_pi_state(q->pi_state);
+ q->pi_state = NULL;
+
+- raw_spin_unlock(q->lock_ptr);
+- kfree(ps);
++ spin_unlock(q->lock_ptr);
+ }
+
+ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+@@ -2599,7 +2581,7 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ */
+ handle_err:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+- raw_spin_unlock(q->lock_ptr);
++ spin_unlock(q->lock_ptr);
+
+ switch (err) {
+ case -EFAULT:
+@@ -2616,7 +2598,7 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ break;
+ }
+
+- raw_spin_lock(q->lock_ptr);
++ spin_lock(q->lock_ptr);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+ /*
+@@ -2730,7 +2712,7 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
+ /*
+ * The task state is guaranteed to be set before another task can
+ * wake it. set_current_state() is implemented using smp_store_mb() and
+- * queue_me() calls raw_spin_unlock() upon completion, both serializing
++ * queue_me() calls spin_unlock() upon completion, both serializing
+ * access to the hash list and forcing another memory barrier.
+ */
+ set_current_state(TASK_INTERRUPTIBLE);
+@@ -3028,7 +3010,15 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
+ * before __rt_mutex_start_proxy_lock() is done.
+ */
+ raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
+- raw_spin_unlock(q.lock_ptr);
++ /*
++ * the migrate_disable() here disables migration in the in_atomic() fast
++ * path which is enabled again in the following spin_unlock(). We have
++ * one migrate_disable() pending in the slow-path which is reversed
++ * after the raw_spin_unlock_irq() where we leave the atomic context.
++ */
++ migrate_disable();
++
++ spin_unlock(q.lock_ptr);
+ /*
+ * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
+ * such that futex_unlock_pi() is guaranteed to observe the waiter when
+@@ -3036,6 +3026,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
+ */
+ ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+ raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
++ migrate_enable();
+
+ if (ret) {
+ if (ret == 1)
+@@ -3049,7 +3040,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
+ ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
+
+ cleanup:
+- raw_spin_lock(q.lock_ptr);
++ spin_lock(q.lock_ptr);
+ /*
+ * If we failed to acquire the lock (deadlock/signal/timeout), we must
+ * first acquire the hb->lock before removing the lock from the
+@@ -3136,7 +3127,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+ return ret;
+
+ hb = hash_futex(&key);
+- raw_spin_lock(&hb->lock);
++ spin_lock(&hb->lock);
+
+ /*
+ * Check waiters first. We do not trust user space values at
+@@ -3170,10 +3161,19 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+ * rt_waiter. Also see the WARN in wake_futex_pi().
+ */
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+- raw_spin_unlock(&hb->lock);
++ /*
++ * Magic trickery for now to make the RT migrate disable
++ * logic happy. The following spin_unlock() happens with
++ * interrupts disabled so the internal migrate_enable()
++ * won't undo the migrate_disable() which was issued when
++ * locking hb->lock.
++ */
++ migrate_disable();
++ spin_unlock(&hb->lock);
+
+ /* drops pi_state->pi_mutex.wait_lock */
+ ret = wake_futex_pi(uaddr, uval, pi_state);
++ migrate_enable();
+
+ put_pi_state(pi_state);
+
+@@ -3209,7 +3209,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+ * owner.
+ */
+ if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
+- raw_spin_unlock(&hb->lock);
++ spin_unlock(&hb->lock);
+ switch (ret) {
+ case -EFAULT:
+ goto pi_faulted;
+@@ -3229,7 +3229,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+ ret = (curval == uval) ? 0 : -EAGAIN;
+
+ out_unlock:
+- raw_spin_unlock(&hb->lock);
++ spin_unlock(&hb->lock);
+ out_putkey:
+ put_futex_key(&key);
+ return ret;
+@@ -3344,7 +3344,7 @@ 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;
+@@ -3402,20 +3402,55 @@ 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);
+
+- raw_spin_lock(&hb->lock);
+- ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
+- raw_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) {
+@@ -3424,17 +3459,15 @@ 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)) {
+- struct futex_pi_state *ps_free;
+-
+- raw_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.
+ */
+- ps_free = __put_pi_state(q.pi_state);
++ put_pi_state(q.pi_state);
+ spin_unlock(&hb2->lock);
+- kfree(ps_free);
+ /*
+ * Adjust the return value. It's either -EFAULT or
+ * success (1) but the caller expects 0 for success.
+@@ -3453,7 +3486,8 @@ 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);
+
+- raw_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;
+
+@@ -4212,7 +4246,7 @@ static int __init futex_init(void)
+ for (i = 0; i < futex_hashsize; i++) {
+ atomic_set(&futex_queues[i].waiters, 0);
+ plist_head_init(&futex_queues[i].chain);
+- raw_spin_lock_init(&futex_queues[i].lock);
++ spin_lock_init(&futex_queues[i].lock);
+ }
+
+ return 0;
+diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
+index 05fcf8a75a51..ded2296f848a 100644
+--- a/kernel/locking/rtmutex.c
++++ b/kernel/locking/rtmutex.c
+@@ -142,6 +142,12 @@ 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 &&
++ waiter != PI_REQUEUE_INPROGRESS;
++}
++
+ /*
+ * We can speed up the acquire/release, if there's no debugging state to be
+ * set up.
+@@ -415,7 +421,8 @@ 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;
+ }
+
+ /*
+@@ -551,7 +558,7 @@ 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;
+
+ /*
+@@ -1321,6 +1328,22 @@ 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;
+@@ -1344,7 +1367,7 @@ 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;
+@@ -1444,7 +1467,7 @@ 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);
+
+@@ -1470,7 +1493,8 @@ 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);
+
+@@ -1506,7 +1530,8 @@ 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;
+ }
+@@ -2324,6 +2349,34 @@ 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 f587e0422d23..8e0c592273e6 100644
+--- a/kernel/locking/rtmutex_common.h
++++ b/kernel/locking/rtmutex_common.h
+@@ -132,6 +132,9 @@ 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,
+ struct task_struct *proxy_owner);
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-21 12:09:15 +0000