Merge branch 'core/urgent' into core/futexes
Merge reason: this branch was on an pre -rc1 base, merge it up to -rc6+
to get the latest upstream fixes.
Conflicts:
kernel/futex.c
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/Documentation/futex-requeue-pi.txt b/Documentation/futex-requeue-pi.txt
new file mode 100644
index 0000000..9dc1ff4
--- /dev/null
+++ b/Documentation/futex-requeue-pi.txt
@@ -0,0 +1,131 @@
+Futex Requeue PI
+----------------
+
+Requeueing of tasks from a non-PI futex to a PI futex requires
+special handling in order to ensure the underlying rt_mutex is never
+left without an owner if it has waiters; doing so would break the PI
+boosting logic [see rt-mutex-desgin.txt] For the purposes of
+brevity, this action will be referred to as "requeue_pi" throughout
+this document. Priority inheritance is abbreviated throughout as
+"PI".
+
+Motivation
+----------
+
+Without requeue_pi, the glibc implementation of
+pthread_cond_broadcast() must resort to waking all the tasks waiting
+on a pthread_condvar and letting them try to sort out which task
+gets to run first in classic thundering-herd formation. An ideal
+implementation would wake the highest-priority waiter, and leave the
+rest to the natural wakeup inherent in unlocking the mutex
+associated with the condvar.
+
+Consider the simplified glibc calls:
+
+/* caller must lock mutex */
+pthread_cond_wait(cond, mutex)
+{
+ lock(cond->__data.__lock);
+ unlock(mutex);
+ do {
+ unlock(cond->__data.__lock);
+ futex_wait(cond->__data.__futex);
+ lock(cond->__data.__lock);
+ } while(...)
+ unlock(cond->__data.__lock);
+ lock(mutex);
+}
+
+pthread_cond_broadcast(cond)
+{
+ lock(cond->__data.__lock);
+ unlock(cond->__data.__lock);
+ futex_requeue(cond->data.__futex, cond->mutex);
+}
+
+Once pthread_cond_broadcast() requeues the tasks, the cond->mutex
+has waiters. Note that pthread_cond_wait() attempts to lock the
+mutex only after it has returned to user space. This will leave the
+underlying rt_mutex with waiters, and no owner, breaking the
+previously mentioned PI-boosting algorithms.
+
+In order to support PI-aware pthread_condvar's, the kernel needs to
+be able to requeue tasks to PI futexes. This support implies that
+upon a successful futex_wait system call, the caller would return to
+user space already holding the PI futex. The glibc implementation
+would be modified as follows:
+
+
+/* caller must lock mutex */
+pthread_cond_wait_pi(cond, mutex)
+{
+ lock(cond->__data.__lock);
+ unlock(mutex);
+ do {
+ unlock(cond->__data.__lock);
+ futex_wait_requeue_pi(cond->__data.__futex);
+ lock(cond->__data.__lock);
+ } while(...)
+ unlock(cond->__data.__lock);
+ /* the kernel acquired the the mutex for us */
+}
+
+pthread_cond_broadcast_pi(cond)
+{
+ lock(cond->__data.__lock);
+ unlock(cond->__data.__lock);
+ futex_requeue_pi(cond->data.__futex, cond->mutex);
+}
+
+The actual glibc implementation will likely test for PI and make the
+necessary changes inside the existing calls rather than creating new
+calls for the PI cases. Similar changes are needed for
+pthread_cond_timedwait() and pthread_cond_signal().
+
+Implementation
+--------------
+
+In order to ensure the rt_mutex has an owner if it has waiters, it
+is necessary for both the requeue code, as well as the waiting code,
+to be able to acquire the rt_mutex before returning to user space.
+The requeue code cannot simply wake the waiter and leave it to
+acquire the rt_mutex as it would open a race window between the
+requeue call returning to user space and the waiter waking and
+starting to run. This is especially true in the uncontended case.
+
+The solution involves two new rt_mutex helper routines,
+rt_mutex_start_proxy_lock() and rt_mutex_finish_proxy_lock(), which
+allow the requeue code to acquire an uncontended rt_mutex on behalf
+of the waiter and to enqueue the waiter on a contended rt_mutex.
+Two new system calls provide the kernel<->user interface to
+requeue_pi: FUTEX_WAIT_REQUEUE_PI and FUTEX_REQUEUE_CMP_PI.
+
+FUTEX_WAIT_REQUEUE_PI is called by the waiter (pthread_cond_wait()
+and pthread_cond_timedwait()) to block on the initial futex and wait
+to be requeued to a PI-aware futex. The implementation is the
+result of a high-speed collision between futex_wait() and
+futex_lock_pi(), with some extra logic to check for the additional
+wake-up scenarios.
+
+FUTEX_REQUEUE_CMP_PI is called by the waker
+(pthread_cond_broadcast() and pthread_cond_signal()) to requeue and
+possibly wake the waiting tasks. Internally, this system call is
+still handled by futex_requeue (by passing requeue_pi=1). Before
+requeueing, futex_requeue() attempts to acquire the requeue target
+PI futex on behalf of the top waiter. If it can, this waiter is
+woken. futex_requeue() then proceeds to requeue the remaining
+nr_wake+nr_requeue tasks to the PI futex, calling
+rt_mutex_start_proxy_lock() prior to each requeue to prepare the
+task as a waiter on the underlying rt_mutex. It is possible that
+the lock can be acquired at this stage as well, if so, the next
+waiter is woken to finish the acquisition of the lock.
+
+FUTEX_REQUEUE_PI accepts nr_wake and nr_requeue as arguments, but
+their sum is all that really matters. futex_requeue() will wake or
+requeue up to nr_wake + nr_requeue tasks. It will wake only as many
+tasks as it can acquire the lock for, which in the majority of cases
+should be 0 as good programming practice dictates that the caller of
+either pthread_cond_broadcast() or pthread_cond_signal() acquire the
+mutex prior to making the call. FUTEX_REQUEUE_PI requires that
+nr_wake=1. nr_requeue should be INT_MAX for broadcast and 0 for
+signal.
diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
index 639ac80..6586572 100644
--- a/arch/sparc/include/asm/thread_info_64.h
+++ b/arch/sparc/include/asm/thread_info_64.h
@@ -102,8 +102,8 @@
#define TI_KERN_CNTD1 0x00000488
#define TI_PCR 0x00000490
#define TI_RESTART_BLOCK 0x00000498
-#define TI_KUNA_REGS 0x000004c0
-#define TI_KUNA_INSN 0x000004c8
+#define TI_KUNA_REGS 0x000004c8
+#define TI_KUNA_INSN 0x000004d0
#define TI_FPREGS 0x00000500
/* We embed this in the uppermost byte of thread_info->flags */
diff --git a/include/linux/futex.h b/include/linux/futex.h
index 3bf5bb5..34956c8 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -23,6 +23,8 @@
#define FUTEX_TRYLOCK_PI 8
#define FUTEX_WAIT_BITSET 9
#define FUTEX_WAKE_BITSET 10
+#define FUTEX_WAIT_REQUEUE_PI 11
+#define FUTEX_CMP_REQUEUE_PI 12
#define FUTEX_PRIVATE_FLAG 128
#define FUTEX_CLOCK_REALTIME 256
@@ -38,6 +40,10 @@
#define FUTEX_TRYLOCK_PI_PRIVATE (FUTEX_TRYLOCK_PI | FUTEX_PRIVATE_FLAG)
#define FUTEX_WAIT_BITSET_PRIVATE (FUTEX_WAIT_BITS | FUTEX_PRIVATE_FLAG)
#define FUTEX_WAKE_BITSET_PRIVATE (FUTEX_WAKE_BITS | FUTEX_PRIVATE_FLAG)
+#define FUTEX_WAIT_REQUEUE_PI_PRIVATE (FUTEX_WAIT_REQUEUE_PI | \
+ FUTEX_PRIVATE_FLAG)
+#define FUTEX_CMP_REQUEUE_PI_PRIVATE (FUTEX_CMP_REQUEUE_PI | \
+ FUTEX_PRIVATE_FLAG)
/*
* Support for robust futexes: the kernel cleans up held futexes at
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index e6b820f..a8cc4e1 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -21,13 +21,14 @@
struct {
unsigned long arg0, arg1, arg2, arg3;
};
- /* For futex_wait */
+ /* For futex_wait and futex_wait_requeue_pi */
struct {
u32 *uaddr;
u32 val;
u32 flags;
u32 bitset;
u64 time;
+ u32 *uaddr2;
} futex;
/* For nanosleep */
struct {
diff --git a/kernel/futex.c b/kernel/futex.c
index d546b2d..476603a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -19,6 +19,10 @@
* PRIVATE futexes by Eric Dumazet
* Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
*
+ * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
+ * Copyright (C) IBM Corporation, 2009
+ * Thanks to Thomas Gleixner for conceptual design and careful reviews.
+ *
* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
* enough at me, Linus for the original (flawed) idea, Matthew
* Kirkwood for proof-of-concept implementation.
@@ -96,8 +100,8 @@
*/
struct futex_q {
struct plist_node list;
- /* There can only be a single waiter */
- wait_queue_head_t waiter;
+ /* Waiter reference */
+ struct task_struct *task;
/* Which hash list lock to use: */
spinlock_t *lock_ptr;
@@ -107,7 +111,9 @@
/* Optional priority inheritance state: */
struct futex_pi_state *pi_state;
- struct task_struct *task;
+
+ /* rt_waiter storage for requeue_pi: */
+ struct rt_mutex_waiter *rt_waiter;
/* Bitset for the optional bitmasked wakeup */
u32 bitset;
@@ -278,6 +284,25 @@
drop_futex_key_refs(key);
}
+/**
+ * futex_top_waiter() - Return the highest priority waiter on a futex
+ * @hb: the hash bucket the futex_q's reside in
+ * @key: the futex key (to distinguish it from other futex futex_q's)
+ *
+ * Must be called with the hb lock held.
+ */
+static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
+ union futex_key *key)
+{
+ struct futex_q *this;
+
+ plist_for_each_entry(this, &hb->chain, list) {
+ if (match_futex(&this->key, key))
+ return this;
+ }
+ return NULL;
+}
+
static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
{
u32 curval;
@@ -539,28 +564,160 @@
return 0;
}
+/**
+ * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
+ * @uaddr: the pi futex user address
+ * @hb: the pi futex hash bucket
+ * @key: the futex key associated with uaddr and hb
+ * @ps: the pi_state pointer where we store the result of the
+ * lookup
+ * @task: the task to perform the atomic lock work for. This will
+ * be "current" except in the case of requeue pi.
+ * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Returns:
+ * 0 - ready to wait
+ * 1 - acquired the lock
+ * <0 - error
+ *
+ * The hb->lock and futex_key refs shall be held by the caller.
+ */
+static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
+ union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct *task, int set_waiters)
+{
+ int lock_taken, ret, ownerdied = 0;
+ u32 uval, newval, curval;
+
+retry:
+ ret = lock_taken = 0;
+
+ /*
+ * To avoid races, we attempt to take the lock here again
+ * (by doing a 0 -> TID atomic cmpxchg), while holding all
+ * the locks. It will most likely not succeed.
+ */
+ newval = task_pid_vnr(task);
+ if (set_waiters)
+ newval |= FUTEX_WAITERS;
+
+ curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
+
+ if (unlikely(curval == -EFAULT))
+ return -EFAULT;
+
+ /*
+ * Detect deadlocks.
+ */
+ if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
+ return -EDEADLK;
+
+ /*
+ * Surprise - we got the lock. Just return to userspace:
+ */
+ if (unlikely(!curval))
+ return 1;
+
+ uval = curval;
+
+ /*
+ * Set the FUTEX_WAITERS flag, so the owner will know it has someone
+ * to wake at the next unlock.
+ */
+ newval = curval | FUTEX_WAITERS;
+
+ /*
+ * There are two cases, where a futex might have no owner (the
+ * owner TID is 0): OWNER_DIED. We take over the futex in this
+ * case. We also do an unconditional take over, when the owner
+ * of the futex died.
+ *
+ * This is safe as we are protected by the hash bucket lock !
+ */
+ if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
+ /* Keep the OWNER_DIED bit */
+ newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
+ ownerdied = 0;
+ lock_taken = 1;
+ }
+
+ curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
+
+ if (unlikely(curval == -EFAULT))
+ return -EFAULT;
+ if (unlikely(curval != uval))
+ goto retry;
+
+ /*
+ * We took the lock due to owner died take over.
+ */
+ if (unlikely(lock_taken))
+ return 1;
+
+ /*
+ * We dont have the lock. Look up the PI state (or create it if
+ * we are the first waiter):
+ */
+ ret = lookup_pi_state(uval, hb, key, ps);
+
+ if (unlikely(ret)) {
+ switch (ret) {
+ case -ESRCH:
+ /*
+ * No owner found for this futex. Check if the
+ * OWNER_DIED bit is set to figure out whether
+ * this is a robust futex or not.
+ */
+ if (get_futex_value_locked(&curval, uaddr))
+ return -EFAULT;
+
+ /*
+ * We simply start over in case of a robust
+ * futex. The code above will take the futex
+ * and return happy.
+ */
+ if (curval & FUTEX_OWNER_DIED) {
+ ownerdied = 1;
+ goto retry;
+ }
+ default:
+ break;
+ }
+ }
+
+ return ret;
+}
+
/*
* The hash bucket lock must be held when this is called.
* Afterwards, the futex_q must not be accessed.
*/
static void wake_futex(struct futex_q *q)
{
+ struct task_struct *p = q->task;
+
+ /*
+ * We set q->lock_ptr = NULL _before_ we wake up the task. If
+ * a non futex wake up happens on another CPU then the task
+ * might exit and p would dereference a non existing task
+ * struct. Prevent this by holding a reference on p across the
+ * wake up.
+ */
+ get_task_struct(p);
+
plist_del(&q->list, &q->list.plist);
/*
- * The lock in wake_up_all() is a crucial memory barrier after the
- * plist_del() and also before assigning to q->lock_ptr.
- */
- wake_up(&q->waiter);
- /*
- * The waiting task can free the futex_q as soon as this is written,
- * without taking any locks. This must come last.
- *
- * A memory barrier is required here to prevent the following store to
- * lock_ptr from getting ahead of the wakeup. Clearing the lock at the
- * end of wake_up() does not prevent this store from moving.
+ * The waiting task can free the futex_q as soon as
+ * q->lock_ptr = NULL is written, without taking any locks. A
+ * memory barrier is required here to prevent the following
+ * store to lock_ptr from getting ahead of the plist_del.
*/
smp_wmb();
q->lock_ptr = NULL;
+
+ wake_up_state(p, TASK_NORMAL);
+ put_task_struct(p);
}
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
@@ -689,7 +846,7 @@
plist_for_each_entry_safe(this, next, head, list) {
if (match_futex (&this->key, &key)) {
- if (this->pi_state) {
+ if (this->pi_state || this->rt_waiter) {
ret = -EINVAL;
break;
}
@@ -802,24 +959,185 @@
return ret;
}
-/*
- * Requeue all waiters hashed on one physical page to another
- * physical page.
+/**
+ * requeue_futex() - Requeue a futex_q from one hb to another
+ * @q: the futex_q to requeue
+ * @hb1: the source hash_bucket
+ * @hb2: the target hash_bucket
+ * @key2: the new key for the requeued futex_q
+ */
+static inline
+void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
+ struct futex_hash_bucket *hb2, union futex_key *key2)
+{
+
+ /*
+ * If key1 and key2 hash to the same bucket, no need to
+ * requeue.
+ */
+ if (likely(&hb1->chain != &hb2->chain)) {
+ plist_del(&q->list, &hb1->chain);
+ plist_add(&q->list, &hb2->chain);
+ q->lock_ptr = &hb2->lock;
+#ifdef CONFIG_DEBUG_PI_LIST
+ q->list.plist.lock = &hb2->lock;
+#endif
+ }
+ get_futex_key_refs(key2);
+ q->key = *key2;
+}
+
+/**
+ * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
+ * q: the futex_q
+ * key: the key of the requeue target futex
+ *
+ * During futex_requeue, with requeue_pi=1, it is possible to acquire the
+ * target futex if it is uncontended or via a lock steal. Set the futex_q key
+ * to the requeue target futex so the waiter can detect the wakeup on the right
+ * futex, but remove it from the hb and NULL the rt_waiter so it can detect
+ * atomic lock acquisition. Must be called with the q->lock_ptr held.
+ */
+static inline
+void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key)
+{
+ drop_futex_key_refs(&q->key);
+ get_futex_key_refs(key);
+ q->key = *key;
+
+ WARN_ON(plist_node_empty(&q->list));
+ plist_del(&q->list, &q->list.plist);
+
+ WARN_ON(!q->rt_waiter);
+ q->rt_waiter = NULL;
+
+ wake_up_state(q->task, TASK_NORMAL);
+}
+
+/**
+ * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
+ * @pifutex: the user address of the to futex
+ * @hb1: the from futex hash bucket, must be locked by the caller
+ * @hb2: the to futex hash bucket, must be locked by the caller
+ * @key1: the from futex key
+ * @key2: the to futex key
+ * @ps: address to store the pi_state pointer
+ * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Try and get the lock on behalf of the top waiter if we can do it atomically.
+ * Wake the top waiter if we succeed. If the caller specified set_waiters,
+ * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
+ * hb1 and hb2 must be held by the caller.
+ *
+ * Returns:
+ * 0 - failed to acquire the lock atomicly
+ * 1 - acquired the lock
+ * <0 - error
+ */
+static int futex_proxy_trylock_atomic(u32 __user *pifutex,
+ struct futex_hash_bucket *hb1,
+ struct futex_hash_bucket *hb2,
+ union futex_key *key1, union futex_key *key2,
+ struct futex_pi_state **ps, int set_waiters)
+{
+ struct futex_q *top_waiter = NULL;
+ u32 curval;
+ int ret;
+
+ if (get_futex_value_locked(&curval, pifutex))
+ return -EFAULT;
+
+ /*
+ * Find the top_waiter and determine if there are additional waiters.
+ * If the caller intends to requeue more than 1 waiter to pifutex,
+ * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
+ * as we have means to handle the possible fault. If not, don't set
+ * the bit unecessarily as it will force the subsequent unlock to enter
+ * the kernel.
+ */
+ top_waiter = futex_top_waiter(hb1, key1);
+
+ /* There are no waiters, nothing for us to do. */
+ if (!top_waiter)
+ return 0;
+
+ /*
+ * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
+ * the contended case or if set_waiters is 1. The pi_state is returned
+ * in ps in contended cases.
+ */
+ ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
+ set_waiters);
+ if (ret == 1)
+ requeue_pi_wake_futex(top_waiter, key2);
+
+ return ret;
+}
+
+/**
+ * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
+ * uaddr1: source futex user address
+ * uaddr2: target futex user address
+ * nr_wake: number of waiters to wake (must be 1 for requeue_pi)
+ * nr_requeue: number of waiters to requeue (0-INT_MAX)
+ * requeue_pi: if we are attempting to requeue from a non-pi futex to a
+ * pi futex (pi to pi requeue is not supported)
+ *
+ * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
+ * uaddr2 atomically on behalf of the top waiter.
+ *
+ * Returns:
+ * >=0 - on success, the number of tasks requeued or woken
+ * <0 - on error
*/
static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
- int nr_wake, int nr_requeue, u32 *cmpval)
+ int nr_wake, int nr_requeue, u32 *cmpval,
+ int requeue_pi)
{
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
+ int drop_count = 0, task_count = 0, ret;
+ struct futex_pi_state *pi_state = NULL;
struct futex_hash_bucket *hb1, *hb2;
struct plist_head *head1;
struct futex_q *this, *next;
- int ret, drop_count = 0;
+ u32 curval2;
+
+ if (requeue_pi) {
+ /*
+ * requeue_pi requires a pi_state, try to allocate it now
+ * without any locks in case it fails.
+ */
+ if (refill_pi_state_cache())
+ return -ENOMEM;
+ /*
+ * requeue_pi must wake as many tasks as it can, up to nr_wake
+ * + nr_requeue, since it acquires the rt_mutex prior to
+ * returning to userspace, so as to not leave the rt_mutex with
+ * waiters and no owner. However, second and third wake-ups
+ * cannot be predicted as they involve race conditions with the
+ * first wake and a fault while looking up the pi_state. Both
+ * pthread_cond_signal() and pthread_cond_broadcast() should
+ * use nr_wake=1.
+ */
+ if (nr_wake != 1)
+ return -EINVAL;
+ }
retry:
+ if (pi_state != NULL) {
+ /*
+ * We will have to lookup the pi_state again, so free this one
+ * to keep the accounting correct.
+ */
+ free_pi_state(pi_state);
+ pi_state = NULL;
+ }
+
ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
- ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_READ);
+ ret = get_futex_key(uaddr2, fshared, &key2,
+ requeue_pi ? VERIFY_WRITE : VERIFY_READ);
if (unlikely(ret != 0))
goto out_put_key1;
@@ -854,32 +1172,99 @@
}
}
+ if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
+ /*
+ * Attempt to acquire uaddr2 and wake the top waiter. If we
+ * intend to requeue waiters, force setting the FUTEX_WAITERS
+ * bit. We force this here where we are able to easily handle
+ * faults rather in the requeue loop below.
+ */
+ ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
+ &key2, &pi_state, nr_requeue);
+
+ /*
+ * At this point the top_waiter has either taken uaddr2 or is
+ * waiting on it. If the former, then the pi_state will not
+ * exist yet, look it up one more time to ensure we have a
+ * reference to it.
+ */
+ if (ret == 1) {
+ WARN_ON(pi_state);
+ task_count++;
+ ret = get_futex_value_locked(&curval2, uaddr2);
+ if (!ret)
+ ret = lookup_pi_state(curval2, hb2, &key2,
+ &pi_state);
+ }
+
+ switch (ret) {
+ case 0:
+ break;
+ case -EFAULT:
+ double_unlock_hb(hb1, hb2);
+ put_futex_key(fshared, &key2);
+ put_futex_key(fshared, &key1);
+ ret = get_user(curval2, uaddr2);
+ if (!ret)
+ goto retry;
+ goto out;
+ case -EAGAIN:
+ /* The owner was exiting, try again. */
+ double_unlock_hb(hb1, hb2);
+ put_futex_key(fshared, &key2);
+ put_futex_key(fshared, &key1);
+ cond_resched();
+ goto retry;
+ default:
+ goto out_unlock;
+ }
+ }
+
head1 = &hb1->chain;
plist_for_each_entry_safe(this, next, head1, list) {
- if (!match_futex (&this->key, &key1))
- continue;
- if (++ret <= nr_wake) {
- wake_futex(this);
- } else {
- /*
- * If key1 and key2 hash to the same bucket, no need to
- * requeue.
- */
- if (likely(head1 != &hb2->chain)) {
- plist_del(&this->list, &hb1->chain);
- plist_add(&this->list, &hb2->chain);
- this->lock_ptr = &hb2->lock;
-#ifdef CONFIG_DEBUG_PI_LIST
- this->list.plist.lock = &hb2->lock;
-#endif
- }
- this->key = key2;
- get_futex_key_refs(&key2);
- drop_count++;
+ if (task_count - nr_wake >= nr_requeue)
+ break;
- if (ret - nr_wake >= nr_requeue)
- break;
+ if (!match_futex(&this->key, &key1))
+ continue;
+
+ WARN_ON(!requeue_pi && this->rt_waiter);
+ WARN_ON(requeue_pi && !this->rt_waiter);
+
+ /*
+ * Wake nr_wake waiters. For requeue_pi, if we acquired the
+ * lock, we already woke the top_waiter. If not, it will be
+ * woken by futex_unlock_pi().
+ */
+ if (++task_count <= nr_wake && !requeue_pi) {
+ wake_futex(this);
+ continue;
}
+
+ /*
+ * Requeue nr_requeue waiters and possibly one more in the case
+ * of requeue_pi if we couldn't acquire the lock atomically.
+ */
+ if (requeue_pi) {
+ /* Prepare the waiter to take the rt_mutex. */
+ atomic_inc(&pi_state->refcount);
+ this->pi_state = pi_state;
+ ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
+ this->rt_waiter,
+ this->task, 1);
+ if (ret == 1) {
+ /* We got the lock. */
+ requeue_pi_wake_futex(this, &key2);
+ continue;
+ } else if (ret) {
+ /* -EDEADLK */
+ this->pi_state = NULL;
+ free_pi_state(pi_state);
+ goto out_unlock;
+ }
+ }
+ requeue_futex(this, hb1, hb2, &key2);
+ drop_count++;
}
out_unlock:
@@ -899,7 +1284,9 @@
out_put_key1:
put_futex_key(fshared, &key1);
out:
- return ret;
+ if (pi_state != NULL)
+ free_pi_state(pi_state);
+ return ret ? ret : task_count;
}
/* The key must be already stored in q->key. */
@@ -907,8 +1294,6 @@
{
struct futex_hash_bucket *hb;
- init_waitqueue_head(&q->waiter);
-
get_futex_key_refs(&q->key);
hb = hash_futex(&q->key);
q->lock_ptr = &hb->lock;
@@ -1119,35 +1504,150 @@
*/
#define FLAGS_SHARED 0x01
#define FLAGS_CLOCKRT 0x02
+#define FLAGS_HAS_TIMEOUT 0x04
static long futex_wait_restart(struct restart_block *restart);
+static long futex_lock_pi_restart(struct restart_block *restart);
-static int futex_wait(u32 __user *uaddr, int fshared,
- u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
+/**
+ * fixup_owner() - Post lock pi_state and corner case management
+ * @uaddr: user address of the futex
+ * @fshared: whether the futex is shared (1) or not (0)
+ * @q: futex_q (contains pi_state and access to the rt_mutex)
+ * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
+ *
+ * After attempting to lock an rt_mutex, this function is called to cleanup
+ * the pi_state owner as well as handle race conditions that may allow us to
+ * acquire the lock. Must be called with the hb lock held.
+ *
+ * Returns:
+ * 1 - success, lock taken
+ * 0 - success, lock not taken
+ * <0 - on error (-EFAULT)
+ */
+static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
+ int locked)
{
- struct task_struct *curr = current;
- struct restart_block *restart;
- DECLARE_WAITQUEUE(wait, curr);
- struct futex_hash_bucket *hb;
- struct futex_q q;
+ struct task_struct *owner;
+ int ret = 0;
+
+ if (locked) {
+ /*
+ * Got the lock. We might not be the anticipated owner if we
+ * did a lock-steal - fix up the PI-state in that case:
+ */
+ if (q->pi_state->owner != current)
+ ret = fixup_pi_state_owner(uaddr, q, current, fshared);
+ goto out;
+ }
+
+ /*
+ * Catch the rare case, where the lock was released when we were on the
+ * way back before we locked the hash bucket.
+ */
+ if (q->pi_state->owner == current) {
+ /*
+ * Try to get the rt_mutex now. This might fail as some other
+ * task acquired the rt_mutex after we removed ourself from the
+ * rt_mutex waiters list.
+ */
+ if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
+ locked = 1;
+ goto out;
+ }
+
+ /*
+ * pi_state is incorrect, some other task did a lock steal and
+ * we returned due to timeout or signal without taking the
+ * rt_mutex. Too late. We can access the rt_mutex_owner without
+ * locking, as the other task is now blocked on the hash bucket
+ * lock. Fix the state up.
+ */
+ owner = rt_mutex_owner(&q->pi_state->pi_mutex);
+ ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
+ goto out;
+ }
+
+ /*
+ * Paranoia check. If we did not take the lock, then we should not be
+ * the owner, nor the pending owner, of the rt_mutex.
+ */
+ if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
+ printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
+ "pi-state %p\n", ret,
+ q->pi_state->pi_mutex.owner,
+ q->pi_state->owner);
+
+out:
+ return ret ? ret : locked;
+}
+
+/**
+ * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
+ * @hb: the futex hash bucket, must be locked by the caller
+ * @q: the futex_q to queue up on
+ * @timeout: the prepared hrtimer_sleeper, or null for no timeout
+ */
+static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
+ struct hrtimer_sleeper *timeout)
+{
+ queue_me(q, hb);
+
+ /*
+ * There might have been scheduling since the queue_me(), as we
+ * cannot hold a spinlock across the get_user() in case it
+ * faults, and we cannot just set TASK_INTERRUPTIBLE state when
+ * queueing ourselves into the futex hash. This code thus has to
+ * rely on the futex_wake() code removing us from hash when it
+ * wakes us up.
+ */
+ set_current_state(TASK_INTERRUPTIBLE);
+
+ /* Arm the timer */
+ if (timeout) {
+ hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
+ if (!hrtimer_active(&timeout->timer))
+ timeout->task = NULL;
+ }
+
+ /*
+ * !plist_node_empty() is safe here without any lock.
+ * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
+ */
+ if (likely(!plist_node_empty(&q->list))) {
+ /*
+ * If the timer has already expired, current will already be
+ * flagged for rescheduling. Only call schedule if there
+ * is no timeout, or if it has yet to expire.
+ */
+ if (!timeout || timeout->task)
+ schedule();
+ }
+ __set_current_state(TASK_RUNNING);
+}
+
+/**
+ * futex_wait_setup() - Prepare to wait on a futex
+ * @uaddr: the futex userspace address
+ * @val: the expected value
+ * @fshared: whether the futex is shared (1) or not (0)
+ * @q: the associated futex_q
+ * @hb: storage for hash_bucket pointer to be returned to caller
+ *
+ * Setup the futex_q and locate the hash_bucket. Get the futex value and
+ * compare it with the expected value. Handle atomic faults internally.
+ * Return with the hb lock held and a q.key reference on success, and unlocked
+ * with no q.key reference on failure.
+ *
+ * Returns:
+ * 0 - uaddr contains val and hb has been locked
+ * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
+ */
+static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
+ struct futex_q *q, struct futex_hash_bucket **hb)
+{
u32 uval;
int ret;
- struct hrtimer_sleeper t;
- int rem = 0;
-
- if (!bitset)
- return -EINVAL;
-
- q.pi_state = NULL;
- q.bitset = bitset;
-retry:
- q.key = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_READ);
- if (unlikely(ret != 0))
- goto out;
-
-retry_private:
- hb = queue_lock(&q);
/*
* Access the page AFTER the hash-bucket is locked.
@@ -1165,95 +1665,83 @@
* A consequence is that futex_wait() can return zero and absorb
* a wakeup when *uaddr != val on entry to the syscall. This is
* rare, but normal.
- *
- * For shared futexes, we hold the mmap semaphore, so the mapping
- * cannot have changed since we looked it up in get_futex_key.
*/
+retry:
+ q->key = FUTEX_KEY_INIT;
+ ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ);
+ if (unlikely(ret != 0))
+ return ret;
+
+retry_private:
+ *hb = queue_lock(q);
+
ret = get_futex_value_locked(&uval, uaddr);
- if (unlikely(ret)) {
- queue_unlock(&q, hb);
+ if (ret) {
+ queue_unlock(q, *hb);
ret = get_user(uval, uaddr);
if (ret)
- goto out_put_key;
+ goto out;
if (!fshared)
goto retry_private;
- put_futex_key(fshared, &q.key);
+ put_futex_key(fshared, &q->key);
goto retry;
}
- ret = -EWOULDBLOCK;
- if (unlikely(uval != val)) {
- queue_unlock(&q, hb);
- goto out_put_key;
+
+ if (uval != val) {
+ queue_unlock(q, *hb);
+ ret = -EWOULDBLOCK;
}
- /* Only actually queue if *uaddr contained val. */
- queue_me(&q, hb);
+out:
+ if (ret)
+ put_futex_key(fshared, &q->key);
+ return ret;
+}
- /*
- * There might have been scheduling since the queue_me(), as we
- * cannot hold a spinlock across the get_user() in case it
- * faults, and we cannot just set TASK_INTERRUPTIBLE state when
- * queueing ourselves into the futex hash. This code thus has to
- * rely on the futex_wake() code removing us from hash when it
- * wakes us up.
- */
+static int futex_wait(u32 __user *uaddr, int fshared,
+ u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
+{
+ struct hrtimer_sleeper timeout, *to = NULL;
+ struct restart_block *restart;
+ struct futex_hash_bucket *hb;
+ struct futex_q q;
+ int ret;
- /* add_wait_queue is the barrier after __set_current_state. */
- __set_current_state(TASK_INTERRUPTIBLE);
- add_wait_queue(&q.waiter, &wait);
- /*
- * !plist_node_empty() is safe here without any lock.
- * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
- */
- if (likely(!plist_node_empty(&q.list))) {
- if (!abs_time)
- schedule();
- else {
- hrtimer_init_on_stack(&t.timer,
- clockrt ? CLOCK_REALTIME :
- CLOCK_MONOTONIC,
- HRTIMER_MODE_ABS);
- hrtimer_init_sleeper(&t, current);
- hrtimer_set_expires_range_ns(&t.timer, *abs_time,
- current->timer_slack_ns);
+ if (!bitset)
+ return -EINVAL;
- hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
- if (!hrtimer_active(&t.timer))
- t.task = NULL;
+ q.pi_state = NULL;
+ q.bitset = bitset;
+ q.rt_waiter = NULL;
- /*
- * the timer could have already expired, in which
- * case current would be flagged for rescheduling.
- * Don't bother calling schedule.
- */
- if (likely(t.task))
- schedule();
+ if (abs_time) {
+ to = &timeout;
- hrtimer_cancel(&t.timer);
-
- /* Flag if a timeout occured */
- rem = (t.task == NULL);
-
- destroy_hrtimer_on_stack(&t.timer);
- }
+ hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
+ CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init_sleeper(to, current);
+ hrtimer_set_expires_range_ns(&to->timer, *abs_time,
+ current->timer_slack_ns);
}
- __set_current_state(TASK_RUNNING);
- /*
- * NOTE: we don't remove ourselves from the waitqueue because
- * we are the only user of it.
- */
+ /* Prepare to wait on uaddr. */
+ ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
+ if (ret)
+ goto out;
+
+ /* queue_me and wait for wakeup, timeout, or a signal. */
+ futex_wait_queue_me(hb, &q, to);
/* If we were woken (and unqueued), we succeeded, whatever. */
ret = 0;
if (!unqueue_me(&q))
goto out_put_key;
ret = -ETIMEDOUT;
- if (rem)
+ if (to && !to->task)
goto out_put_key;
/*
@@ -1270,7 +1758,7 @@
restart->futex.val = val;
restart->futex.time = abs_time->tv64;
restart->futex.bitset = bitset;
- restart->futex.flags = 0;
+ restart->futex.flags = FLAGS_HAS_TIMEOUT;
if (fshared)
restart->futex.flags |= FLAGS_SHARED;
@@ -1282,6 +1770,10 @@
out_put_key:
put_futex_key(fshared, &q.key);
out:
+ if (to) {
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+ }
return ret;
}
@@ -1290,13 +1782,16 @@
{
u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
int fshared = 0;
- ktime_t t;
+ ktime_t t, *tp = NULL;
- t.tv64 = restart->futex.time;
+ if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
+ t.tv64 = restart->futex.time;
+ tp = &t;
+ }
restart->fn = do_no_restart_syscall;
if (restart->futex.flags & FLAGS_SHARED)
fshared = 1;
- return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
+ return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
restart->futex.bitset,
restart->futex.flags & FLAGS_CLOCKRT);
}
@@ -1312,11 +1807,10 @@
int detect, ktime_t *time, int trylock)
{
struct hrtimer_sleeper timeout, *to = NULL;
- struct task_struct *curr = current;
struct futex_hash_bucket *hb;
- u32 uval, newval, curval;
+ u32 uval;
struct futex_q q;
- int ret, lock_taken, ownerdied = 0;
+ int res, ret;
if (refill_pi_state_cache())
return -ENOMEM;
@@ -1330,6 +1824,7 @@
}
q.pi_state = NULL;
+ q.rt_waiter = NULL;
retry:
q.key = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
@@ -1339,81 +1834,15 @@
retry_private:
hb = queue_lock(&q);
-retry_locked:
- ret = lock_taken = 0;
-
- /*
- * To avoid races, we attempt to take the lock here again
- * (by doing a 0 -> TID atomic cmpxchg), while holding all
- * the locks. It will most likely not succeed.
- */
- newval = task_pid_vnr(current);
-
- curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
-
- if (unlikely(curval == -EFAULT))
- goto uaddr_faulted;
-
- /*
- * Detect deadlocks. In case of REQUEUE_PI this is a valid
- * situation and we return success to user space.
- */
- if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(current))) {
- ret = -EDEADLK;
- goto out_unlock_put_key;
- }
-
- /*
- * Surprise - we got the lock. Just return to userspace:
- */
- if (unlikely(!curval))
- goto out_unlock_put_key;
-
- uval = curval;
-
- /*
- * Set the WAITERS flag, so the owner will know it has someone
- * to wake at next unlock
- */
- newval = curval | FUTEX_WAITERS;
-
- /*
- * There are two cases, where a futex might have no owner (the
- * owner TID is 0): OWNER_DIED. We take over the futex in this
- * case. We also do an unconditional take over, when the owner
- * of the futex died.
- *
- * This is safe as we are protected by the hash bucket lock !
- */
- if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
- /* Keep the OWNER_DIED bit */
- newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);
- ownerdied = 0;
- lock_taken = 1;
- }
-
- curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
-
- if (unlikely(curval == -EFAULT))
- goto uaddr_faulted;
- if (unlikely(curval != uval))
- goto retry_locked;
-
- /*
- * We took the lock due to owner died take over.
- */
- if (unlikely(lock_taken))
- goto out_unlock_put_key;
-
- /*
- * We dont have the lock. Look up the PI state (or create it if
- * we are the first waiter):
- */
- ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
-
+ ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
if (unlikely(ret)) {
switch (ret) {
-
+ case 1:
+ /* We got the lock. */
+ ret = 0;
+ goto out_unlock_put_key;
+ case -EFAULT:
+ goto uaddr_faulted;
case -EAGAIN:
/*
* Task is exiting and we just wait for the
@@ -1423,25 +1852,6 @@
put_futex_key(fshared, &q.key);
cond_resched();
goto retry;
-
- case -ESRCH:
- /*
- * No owner found for this futex. Check if the
- * OWNER_DIED bit is set to figure out whether
- * this is a robust futex or not.
- */
- if (get_futex_value_locked(&curval, uaddr))
- goto uaddr_faulted;
-
- /*
- * We simply start over in case of a robust
- * futex. The code above will take the futex
- * and return happy.
- */
- if (curval & FUTEX_OWNER_DIED) {
- ownerdied = 1;
- goto retry_locked;
- }
default:
goto out_unlock_put_key;
}
@@ -1465,71 +1875,21 @@
}
spin_lock(q.lock_ptr);
-
- if (!ret) {
- /*
- * Got the lock. We might not be the anticipated owner
- * if we did a lock-steal - fix up the PI-state in
- * that case:
- */
- if (q.pi_state->owner != curr)
- ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
- } else {
- /*
- * Catch the rare case, where the lock was released
- * when we were on the way back before we locked the
- * hash bucket.
- */
- if (q.pi_state->owner == curr) {
- /*
- * Try to get the rt_mutex now. This might
- * fail as some other task acquired the
- * rt_mutex after we removed ourself from the
- * rt_mutex waiters list.
- */
- if (rt_mutex_trylock(&q.pi_state->pi_mutex))
- ret = 0;
- else {
- /*
- * pi_state is incorrect, some other
- * task did a lock steal and we
- * returned due to timeout or signal
- * without taking the rt_mutex. Too
- * late. We can access the
- * rt_mutex_owner without locking, as
- * the other task is now blocked on
- * the hash bucket lock. Fix the state
- * up.
- */
- struct task_struct *owner;
- int res;
-
- owner = rt_mutex_owner(&q.pi_state->pi_mutex);
- res = fixup_pi_state_owner(uaddr, &q, owner,
- fshared);
-
- /* propagate -EFAULT, if the fixup failed */
- if (res)
- ret = res;
- }
- } else {
- /*
- * Paranoia check. If we did not take the lock
- * in the trylock above, then we should not be
- * the owner of the rtmutex, neither the real
- * nor the pending one:
- */
- if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
- printk(KERN_ERR "futex_lock_pi: ret = %d "
- "pi-mutex: %p pi-state %p\n", ret,
- q.pi_state->pi_mutex.owner,
- q.pi_state->owner);
- }
- }
+ /*
+ * Fixup the pi_state owner and possibly acquire the lock if we
+ * haven't already.
+ */
+ res = fixup_owner(uaddr, fshared, &q, !ret);
+ /*
+ * If fixup_owner() returned an error, proprogate that. If it acquired
+ * the lock, clear our -ETIMEDOUT or -EINTR.
+ */
+ if (res)
+ ret = (res < 0) ? res : 0;
/*
- * If fixup_pi_state_owner() faulted and was unable to handle the
- * fault, unlock it and return the fault to userspace.
+ * If fixup_owner() faulted and was unable to handle the fault, unlock
+ * it and return the fault to userspace.
*/
if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
rt_mutex_unlock(&q.pi_state->pi_mutex);
@@ -1537,9 +1897,7 @@
/* Unqueue and drop the lock */
unqueue_me_pi(&q);
- if (to)
- destroy_hrtimer_on_stack(&to->timer);
- return ret != -EINTR ? ret : -ERESTARTNOINTR;
+ goto out;
out_unlock_put_key:
queue_unlock(&q, hb);
@@ -1549,7 +1907,7 @@
out:
if (to)
destroy_hrtimer_on_stack(&to->timer);
- return ret;
+ return ret != -EINTR ? ret : -ERESTARTNOINTR;
uaddr_faulted:
/*
@@ -1572,6 +1930,20 @@
goto retry;
}
+static long futex_lock_pi_restart(struct restart_block *restart)
+{
+ u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
+ ktime_t t, *tp = NULL;
+ int fshared = restart->futex.flags & FLAGS_SHARED;
+
+ if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
+ t.tv64 = restart->futex.time;
+ tp = &t;
+ }
+ restart->fn = do_no_restart_syscall;
+
+ return (long)futex_lock_pi(uaddr, fshared, restart->futex.val, tp, 0);
+}
/*
* Userspace attempted a TID -> 0 atomic transition, and failed.
@@ -1674,6 +2046,252 @@
return ret;
}
+/**
+ * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
+ * @hb: the hash_bucket futex_q was original enqueued on
+ * @q: the futex_q woken while waiting to be requeued
+ * @key2: the futex_key of the requeue target futex
+ * @timeout: the timeout associated with the wait (NULL if none)
+ *
+ * Detect if the task was woken on the initial futex as opposed to the requeue
+ * target futex. If so, determine if it was a timeout or a signal that caused
+ * the wakeup and return the appropriate error code to the caller. Must be
+ * called with the hb lock held.
+ *
+ * Returns
+ * 0 - no early wakeup detected
+ * <0 - -ETIMEDOUT or -ERESTARTSYS (FIXME: or ERESTARTNOINTR?)
+ */
+static inline
+int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
+ struct futex_q *q, union futex_key *key2,
+ struct hrtimer_sleeper *timeout)
+{
+ int ret = 0;
+
+ /*
+ * With the hb lock held, we avoid races while we process the wakeup.
+ * We only need to hold hb (and not hb2) to ensure atomicity as the
+ * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
+ * It can't be requeued from uaddr2 to something else since we don't
+ * support a PI aware source futex for requeue.
+ */
+ if (!match_futex(&q->key, key2)) {
+ WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
+ /*
+ * We were woken prior to requeue by a timeout or a signal.
+ * Unqueue the futex_q and determine which it was.
+ */
+ plist_del(&q->list, &q->list.plist);
+ drop_futex_key_refs(&q->key);
+
+ if (timeout && !timeout->task)
+ ret = -ETIMEDOUT;
+ else {
+ /*
+ * We expect signal_pending(current), but another
+ * thread may have handled it for us already.
+ */
+ /* FIXME: ERESTARTSYS or ERESTARTNOINTR? Do we care if
+ * the user specified SA_RESTART or not? */
+ ret = -ERESTARTSYS;
+ }
+ }
+ return ret;
+}
+
+/**
+ * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
+ * @uaddr: the futex we initialyl wait on (non-pi)
+ * @fshared: whether the futexes are shared (1) or not (0). They must be
+ * the same type, no requeueing from private to shared, etc.
+ * @val: the expected value of uaddr
+ * @abs_time: absolute timeout
+ * @bitset: 32 bit wakeup bitset set by userspace, defaults to all.
+ * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
+ * @uaddr2: the pi futex we will take prior to returning to user-space
+ *
+ * The caller will wait on uaddr and will be requeued by futex_requeue() to
+ * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
+ * complete the acquisition of the rt_mutex prior to returning to userspace.
+ * This ensures the rt_mutex maintains an owner when it has waiters; without
+ * one, the pi logic wouldn't know which task to boost/deboost, if there was a
+ * need to.
+ *
+ * We call schedule in futex_wait_queue_me() when we enqueue and return there
+ * via the following:
+ * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
+ * 2) wakeup on uaddr2 after a requeue and subsequent unlock
+ * 3) signal (before or after requeue)
+ * 4) timeout (before or after requeue)
+ *
+ * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
+ *
+ * If 2, we may then block on trying to take the rt_mutex and return via:
+ * 5) successful lock
+ * 6) signal
+ * 7) timeout
+ * 8) other lock acquisition failure
+ *
+ * If 6, we setup a restart_block with futex_lock_pi() as the function.
+ *
+ * If 4 or 7, we cleanup and return with -ETIMEDOUT.
+ *
+ * Returns:
+ * 0 - On success
+ * <0 - On error
+ */
+static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
+ u32 val, ktime_t *abs_time, u32 bitset,
+ int clockrt, u32 __user *uaddr2)
+{
+ struct hrtimer_sleeper timeout, *to = NULL;
+ struct rt_mutex_waiter rt_waiter;
+ struct rt_mutex *pi_mutex = NULL;
+ struct restart_block *restart;
+ struct futex_hash_bucket *hb;
+ union futex_key key2;
+ struct futex_q q;
+ int res, ret;
+ u32 uval;
+
+ if (!bitset)
+ return -EINVAL;
+
+ if (abs_time) {
+ to = &timeout;
+ hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
+ CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init_sleeper(to, current);
+ hrtimer_set_expires_range_ns(&to->timer, *abs_time,
+ current->timer_slack_ns);
+ }
+
+ /*
+ * The waiter is allocated on our stack, manipulated by the requeue
+ * code while we sleep on uaddr.
+ */
+ debug_rt_mutex_init_waiter(&rt_waiter);
+ rt_waiter.task = NULL;
+
+ q.pi_state = NULL;
+ q.bitset = bitset;
+ q.rt_waiter = &rt_waiter;
+
+ key2 = FUTEX_KEY_INIT;
+ ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
+ if (unlikely(ret != 0))
+ goto out;
+
+ /* Prepare to wait on uaddr. */
+ ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
+ if (ret) {
+ put_futex_key(fshared, &key2);
+ goto out;
+ }
+
+ /* 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;
+
+ /*
+ * 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 acquition by the requeue code.
+ */
+
+ /* Check if the requeue code acquired the second futex for us. */
+ if (!q.rt_waiter) {
+ /*
+ * Got the lock. We might not be the anticipated owner if we
+ * 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);
+ ret = fixup_pi_state_owner(uaddr2, &q, current,
+ fshared);
+ spin_unlock(q.lock_ptr);
+ }
+ } else {
+ /*
+ * We have been woken up by futex_unlock_pi(), a timeout, or a
+ * signal. futex_unlock_pi() will not destroy the lock_ptr nor
+ * the pi_state.
+ */
+ WARN_ON(!&q.pi_state);
+ pi_mutex = &q.pi_state->pi_mutex;
+ ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
+ debug_rt_mutex_free_waiter(&rt_waiter);
+
+ spin_lock(q.lock_ptr);
+ /*
+ * Fixup the pi_state owner and possibly acquire the lock if we
+ * haven't already.
+ */
+ res = fixup_owner(uaddr2, fshared, &q, !ret);
+ /*
+ * If fixup_owner() returned an error, proprogate that. If it
+ * acquired the lock, clear our -ETIMEDOUT or -EINTR.
+ */
+ if (res)
+ ret = (res < 0) ? res : 0;
+
+ /* Unqueue and drop the lock. */
+ unqueue_me_pi(&q);
+ }
+
+ /*
+ * If fixup_pi_state_owner() faulted and was unable to handle the
+ * fault, unlock the rt_mutex and return the fault to userspace.
+ */
+ if (ret == -EFAULT) {
+ if (rt_mutex_owner(pi_mutex) == current)
+ rt_mutex_unlock(pi_mutex);
+ } else if (ret == -EINTR) {
+ ret = -EFAULT;
+ if (get_user(uval, uaddr2))
+ goto out_put_keys;
+
+ /*
+ * We've already been requeued, so restart by calling
+ * futex_lock_pi() directly, rather then returning to this
+ * function.
+ */
+ ret = -ERESTART_RESTARTBLOCK;
+ restart = ¤t_thread_info()->restart_block;
+ restart->fn = futex_lock_pi_restart;
+ restart->futex.uaddr = (u32 *)uaddr2;
+ restart->futex.val = uval;
+ restart->futex.flags = 0;
+ if (abs_time) {
+ restart->futex.flags |= FLAGS_HAS_TIMEOUT;
+ restart->futex.time = abs_time->tv64;
+ }
+
+ if (fshared)
+ restart->futex.flags |= FLAGS_SHARED;
+ if (clockrt)
+ restart->futex.flags |= FLAGS_CLOCKRT;
+ }
+
+out_put_keys:
+ put_futex_key(fshared, &q.key);
+ put_futex_key(fshared, &key2);
+
+out:
+ if (to) {
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+ }
+ return ret;
+}
+
/*
* Support for robust futexes: the kernel cleans up held futexes at
* thread exit time.
@@ -1896,7 +2514,7 @@
fshared = 1;
clockrt = op & FUTEX_CLOCK_REALTIME;
- if (clockrt && cmd != FUTEX_WAIT_BITSET)
+ if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
return -ENOSYS;
switch (cmd) {
@@ -1911,10 +2529,11 @@
ret = futex_wake(uaddr, fshared, val, val3);
break;
case FUTEX_REQUEUE:
- ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL);
+ ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
break;
case FUTEX_CMP_REQUEUE:
- ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3);
+ ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
+ 0);
break;
case FUTEX_WAKE_OP:
ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
@@ -1931,6 +2550,15 @@
if (futex_cmpxchg_enabled)
ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
break;
+ case FUTEX_WAIT_REQUEUE_PI:
+ val3 = FUTEX_BITSET_MATCH_ANY;
+ ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
+ clockrt, uaddr2);
+ break;
+ case FUTEX_CMP_REQUEUE_PI:
+ ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
+ 1);
+ break;
default:
ret = -ENOSYS;
}
@@ -1948,7 +2576,8 @@
int cmd = op & FUTEX_CMD_MASK;
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
- cmd == FUTEX_WAIT_BITSET)) {
+ cmd == FUTEX_WAIT_BITSET ||
+ cmd == FUTEX_WAIT_REQUEUE_PI)) {
if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
return -EFAULT;
if (!timespec_valid(&ts))
@@ -1960,11 +2589,11 @@
tp = &t;
}
/*
- * requeue parameter in 'utime' if cmd == FUTEX_REQUEUE.
+ * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
* number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
*/
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
- cmd == FUTEX_WAKE_OP)
+ cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
val2 = (u32) (unsigned long) utime;
return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 69d9cb9..fec77e7 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -300,7 +300,8 @@
* assigned pending owner [which might not have taken the
* lock yet]:
*/
-static inline int try_to_steal_lock(struct rt_mutex *lock)
+static inline int try_to_steal_lock(struct rt_mutex *lock,
+ struct task_struct *task)
{
struct task_struct *pendowner = rt_mutex_owner(lock);
struct rt_mutex_waiter *next;
@@ -309,11 +310,11 @@
if (!rt_mutex_owner_pending(lock))
return 0;
- if (pendowner == current)
+ if (pendowner == task)
return 1;
spin_lock_irqsave(&pendowner->pi_lock, flags);
- if (current->prio >= pendowner->prio) {
+ if (task->prio >= pendowner->prio) {
spin_unlock_irqrestore(&pendowner->pi_lock, flags);
return 0;
}
@@ -338,21 +339,21 @@
* We are going to steal the lock and a waiter was
* enqueued on the pending owners pi_waiters queue. So
* we have to enqueue this waiter into
- * current->pi_waiters list. This covers the case,
- * where current is boosted because it holds another
+ * task->pi_waiters list. This covers the case,
+ * where task is boosted because it holds another
* lock and gets unboosted because the booster is
* interrupted, so we would delay a waiter with higher
- * priority as current->normal_prio.
+ * priority as task->normal_prio.
*
* Note: in the rare case of a SCHED_OTHER task changing
* its priority and thus stealing the lock, next->task
- * might be current:
+ * might be task:
*/
- if (likely(next->task != current)) {
- spin_lock_irqsave(¤t->pi_lock, flags);
- plist_add(&next->pi_list_entry, ¤t->pi_waiters);
- __rt_mutex_adjust_prio(current);
- spin_unlock_irqrestore(¤t->pi_lock, flags);
+ if (likely(next->task != task)) {
+ spin_lock_irqsave(&task->pi_lock, flags);
+ plist_add(&next->pi_list_entry, &task->pi_waiters);
+ __rt_mutex_adjust_prio(task);
+ spin_unlock_irqrestore(&task->pi_lock, flags);
}
return 1;
}
@@ -389,7 +390,7 @@
*/
mark_rt_mutex_waiters(lock);
- if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
+ if (rt_mutex_owner(lock) && !try_to_steal_lock(lock, current))
return 0;
/* We got the lock. */
@@ -411,6 +412,7 @@
*/
static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
+ struct task_struct *task,
int detect_deadlock)
{
struct task_struct *owner = rt_mutex_owner(lock);
@@ -418,21 +420,21 @@
unsigned long flags;
int chain_walk = 0, res;
- spin_lock_irqsave(¤t->pi_lock, flags);
- __rt_mutex_adjust_prio(current);
- waiter->task = current;
+ spin_lock_irqsave(&task->pi_lock, flags);
+ __rt_mutex_adjust_prio(task);
+ waiter->task = task;
waiter->lock = lock;
- plist_node_init(&waiter->list_entry, current->prio);
- plist_node_init(&waiter->pi_list_entry, current->prio);
+ plist_node_init(&waiter->list_entry, task->prio);
+ plist_node_init(&waiter->pi_list_entry, task->prio);
/* Get the top priority waiter on the lock */
if (rt_mutex_has_waiters(lock))
top_waiter = rt_mutex_top_waiter(lock);
plist_add(&waiter->list_entry, &lock->wait_list);
- current->pi_blocked_on = waiter;
+ task->pi_blocked_on = waiter;
- spin_unlock_irqrestore(¤t->pi_lock, flags);
+ spin_unlock_irqrestore(&task->pi_lock, flags);
if (waiter == rt_mutex_top_waiter(lock)) {
spin_lock_irqsave(&owner->pi_lock, flags);
@@ -460,7 +462,7 @@
spin_unlock(&lock->wait_lock);
res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
- current);
+ task);
spin_lock(&lock->wait_lock);
@@ -605,6 +607,85 @@
rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
}
+/**
+ * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
+ * @lock: the rt_mutex to take
+ * @state: the state the task should block in (TASK_INTERRUPTIBLE
+ * or TASK_UNINTERRUPTIBLE)
+ * @timeout: the pre-initialized and started timer, or NULL for none
+ * @waiter: the pre-initialized rt_mutex_waiter
+ * @detect_deadlock: passed to task_blocks_on_rt_mutex
+ *
+ * lock->wait_lock must be held by the caller.
+ */
+static int __sched
+__rt_mutex_slowlock(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ struct rt_mutex_waiter *waiter,
+ int detect_deadlock)
+{
+ int ret = 0;
+
+ for (;;) {
+ /* Try to acquire the lock: */
+ if (try_to_take_rt_mutex(lock))
+ break;
+
+ /*
+ * TASK_INTERRUPTIBLE checks for signals and
+ * timeout. Ignored otherwise.
+ */
+ if (unlikely(state == TASK_INTERRUPTIBLE)) {
+ /* Signal pending? */
+ if (signal_pending(current))
+ ret = -EINTR;
+ if (timeout && !timeout->task)
+ ret = -ETIMEDOUT;
+ if (ret)
+ break;
+ }
+
+ /*
+ * waiter->task is NULL the first time we come here and
+ * when we have been woken up by the previous owner
+ * but the lock got stolen by a higher prio task.
+ */
+ if (!waiter->task) {
+ ret = task_blocks_on_rt_mutex(lock, waiter, current,
+ detect_deadlock);
+ /*
+ * If we got woken up by the owner then start loop
+ * all over without going into schedule to try
+ * to get the lock now:
+ */
+ if (unlikely(!waiter->task)) {
+ /*
+ * Reset the return value. We might
+ * have returned with -EDEADLK and the
+ * owner released the lock while we
+ * were walking the pi chain.
+ */
+ ret = 0;
+ continue;
+ }
+ if (unlikely(ret))
+ break;
+ }
+
+ spin_unlock(&lock->wait_lock);
+
+ debug_rt_mutex_print_deadlock(waiter);
+
+ if (waiter->task)
+ schedule_rt_mutex(lock);
+
+ spin_lock(&lock->wait_lock);
+ set_current_state(state);
+ }
+
+ return ret;
+}
+
/*
* Slow path lock function:
*/
@@ -636,62 +717,8 @@
timeout->task = NULL;
}
- for (;;) {
- /* Try to acquire the lock: */
- if (try_to_take_rt_mutex(lock))
- break;
-
- /*
- * TASK_INTERRUPTIBLE checks for signals and
- * timeout. Ignored otherwise.
- */
- if (unlikely(state == TASK_INTERRUPTIBLE)) {
- /* Signal pending? */
- if (signal_pending(current))
- ret = -EINTR;
- if (timeout && !timeout->task)
- ret = -ETIMEDOUT;
- if (ret)
- break;
- }
-
- /*
- * waiter.task is NULL the first time we come here and
- * when we have been woken up by the previous owner
- * but the lock got stolen by a higher prio task.
- */
- if (!waiter.task) {
- ret = task_blocks_on_rt_mutex(lock, &waiter,
- detect_deadlock);
- /*
- * If we got woken up by the owner then start loop
- * all over without going into schedule to try
- * to get the lock now:
- */
- if (unlikely(!waiter.task)) {
- /*
- * Reset the return value. We might
- * have returned with -EDEADLK and the
- * owner released the lock while we
- * were walking the pi chain.
- */
- ret = 0;
- continue;
- }
- if (unlikely(ret))
- break;
- }
-
- spin_unlock(&lock->wait_lock);
-
- debug_rt_mutex_print_deadlock(&waiter);
-
- if (waiter.task)
- schedule_rt_mutex(lock);
-
- spin_lock(&lock->wait_lock);
- set_current_state(state);
- }
+ ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
+ detect_deadlock);
set_current_state(TASK_RUNNING);
@@ -986,6 +1013,59 @@
}
/**
+ * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
+ * @lock: the rt_mutex to take
+ * @waiter: the pre-initialized rt_mutex_waiter
+ * @task: the task to prepare
+ * @detect_deadlock: perform deadlock detection (1) or not (0)
+ *
+ * Returns:
+ * 0 - task blocked on lock
+ * 1 - acquired the lock for task, caller should wake it up
+ * <0 - error
+ *
+ * Special API call for FUTEX_REQUEUE_PI support.
+ */
+int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct task_struct *task, int detect_deadlock)
+{
+ int ret;
+
+ spin_lock(&lock->wait_lock);
+
+ mark_rt_mutex_waiters(lock);
+
+ if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
+ /* We got the lock for task. */
+ debug_rt_mutex_lock(lock);
+
+ rt_mutex_set_owner(lock, task, 0);
+
+ rt_mutex_deadlock_account_lock(lock, task);
+ return 1;
+ }
+
+ ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
+
+
+ if (ret && !waiter->task) {
+ /*
+ * Reset the return value. We might have
+ * returned with -EDEADLK and the owner
+ * released the lock while we were walking the
+ * pi chain. Let the waiter sort it out.
+ */
+ ret = 0;
+ }
+ spin_unlock(&lock->wait_lock);
+
+ debug_rt_mutex_print_deadlock(waiter);
+
+ return ret;
+}
+
+/**
* rt_mutex_next_owner - return the next owner of the lock
*
* @lock: the rt lock query
@@ -1004,3 +1084,57 @@
return rt_mutex_top_waiter(lock)->task;
}
+
+/**
+ * rt_mutex_finish_proxy_lock() - Complete lock acquisition
+ * @lock: the rt_mutex we were woken on
+ * @to: the timeout, null if none. hrtimer should already have
+ * been started.
+ * @waiter: the pre-initialized rt_mutex_waiter
+ * @detect_deadlock: perform deadlock detection (1) or not (0)
+ *
+ * Complete the lock acquisition started our behalf by another thread.
+ *
+ * Returns:
+ * 0 - success
+ * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
+ *
+ * Special API call for PI-futex requeue support
+ */
+int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
+ struct hrtimer_sleeper *to,
+ struct rt_mutex_waiter *waiter,
+ int detect_deadlock)
+{
+ int ret;
+
+ spin_lock(&lock->wait_lock);
+
+ set_current_state(TASK_INTERRUPTIBLE);
+
+ ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
+ detect_deadlock);
+
+ set_current_state(TASK_RUNNING);
+
+ if (unlikely(waiter->task))
+ remove_waiter(lock, waiter);
+
+ /*
+ * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
+ * have to fix that up.
+ */
+ fixup_rt_mutex_waiters(lock);
+
+ spin_unlock(&lock->wait_lock);
+
+ /*
+ * Readjust priority, when we did not get the lock. We might have been
+ * the pending owner and boosted. Since we did not take the lock, the
+ * PI boost has to go.
+ */
+ if (unlikely(ret))
+ rt_mutex_adjust_prio(current);
+
+ return ret;
+}
diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h
index e124bf5..97a2f81 100644
--- a/kernel/rtmutex_common.h
+++ b/kernel/rtmutex_common.h
@@ -120,6 +120,14 @@
struct task_struct *proxy_owner);
extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
struct task_struct *proxy_owner);
+extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct task_struct *task,
+ int detect_deadlock);
+extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
+ struct hrtimer_sleeper *to,
+ struct rt_mutex_waiter *waiter,
+ int detect_deadlock);
#ifdef CONFIG_DEBUG_RT_MUTEXES
# include "rtmutex-debug.h"