Hi,
With the introduction of the PI-futex (used for the PI-pthread_mutex in
the glibc), the current futex_requeue optimization (*) can not be used
any more if the pthread_mutex used with the pthread-condvar is a PI-mutex.
(*) this optimization is used in pthread_cond_broadcast.
To use this optimization with PI-mutex, we need a function that
re-queues some threads from a normal futex to a PI-futex (see why in
this discussion:
http://marc.theaimsgroup.com/?l=linux-kernel&m=115020355126851&w=2 )
Here is a proposal of an implementation of futex_requeue_pi.
(Only the 32-bits version has been implemented for now)
To use or test this patch with pthreads, you will need to patch the
glibc. The glibc patch is available here:
http://www.bullopensource.org/posix/pi-futex/glibc_requeue_pi.diff
(Only available for ix86 architecture)
or use the generic pthread_cond_broadcast.c file
(patch here:
http://www.bullopensource.org/posix/pi-futex/glibc_pth_broadcast_c_file.diff
)
I'll send some explanations in a separate mail.
The code has been tested and seems to work fine but is probably, heu,
"perfectible" ...
So, comments, suggestions, feedbacks are welcome.
---
include/linux/futex.h | 8
kernel/futex.c | 583 ++++++++++++++++++++++++++++++++++++++++++------
kernel/futex_compat.c | 3
kernel/rtmutex.c | 43 ---
kernel/rtmutex_common.h | 36 ++
5 files changed, 575 insertions(+), 98 deletions(-)
---
Signed-off-by: Pierre Peiffer <[email protected]>
---
Index: linux-2.6/include/linux/futex.h
===================================================================
--- linux-2.6.orig/include/linux/futex.h 2006-12-12 16:38:00.000000000 +0100
+++ linux-2.6/include/linux/futex.h 2006-12-12 16:43:53.000000000 +0100
@@ -15,6 +15,7 @@
#define FUTEX_LOCK_PI 6
#define FUTEX_UNLOCK_PI 7
#define FUTEX_TRYLOCK_PI 8
+#define FUTEX_CMP_REQUEUE_PI 9
/*
* Support for robust futexes: the kernel cleans up held futexes at
@@ -83,9 +84,14 @@ struct robust_list_head {
#define FUTEX_OWNER_DIED 0x40000000
/*
+ * Some processes have been requeued on this PI-futex
+ */
+#define FUTEX_WAITER_REQUEUED 0x20000000
+
+/*
* The rest of the robust-futex field is for the TID:
*/
-#define FUTEX_TID_MASK 0x3fffffff
+#define FUTEX_TID_MASK 0x1fffffff
/*
* This limit protects against a deliberately circular list.
Index: linux-2.6/kernel/futex.c
===================================================================
--- linux-2.6.orig/kernel/futex.c 2006-12-12 16:38:00.000000000 +0100
+++ linux-2.6/kernel/futex.c 2006-12-13 13:41:29.000000000 +0100
@@ -53,6 +53,12 @@
#include "rtmutex_common.h"
+#ifdef CONFIG_DEBUG_RT_MUTEXES
+# include "rtmutex-debug.h"
+#else
+# include "rtmutex.h"
+#endif
+
#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
/*
@@ -128,6 +134,10 @@ struct futex_q {
/* Optional priority inheritance state: */
struct futex_pi_state *pi_state;
struct task_struct *task;
+
+ /* This waiter is used in case of requeue from a
+ normal futex to a PI-futex */
+ struct rt_mutex_waiter waiter;
};
/*
@@ -249,6 +259,24 @@ static int get_futex_key(void *uaddr, un
}
/*
+ * Retrieve the original address used to compute this key
+ */
+static void *get_futex_address(union futex_key *key)
+{
+ void *uaddr;
+
+ if (key->both.offset & 1)
+ /* shared mapping */
+ uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT)
+ + key->shared.offset - 1);
+ else
+ /* private mapping */
+ uaddr = (void*)(key->private.address + key->private.offset);
+
+ return uaddr;
+}
+
+/*
* Take a reference to the resource addressed by a key.
* Can be called while holding spinlocks.
*
@@ -463,7 +491,8 @@ void exit_pi_state_list(struct task_stru
}
static int
-lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
+lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
+ union futex_key *key, struct futex_pi_state **ps)
{
struct futex_pi_state *pi_state = NULL;
struct futex_q *this, *next;
@@ -474,7 +503,7 @@ lookup_pi_state(u32 uval, struct futex_h
head = &hb->chain;
plist_for_each_entry_safe(this, next, head, list) {
- if (match_futex(&this->key, &me->key)) {
+ if (match_futex(&this->key, key)) {
/*
* Another waiter already exists - bump up
* the refcount and return its pi_state:
@@ -489,7 +518,7 @@ lookup_pi_state(u32 uval, struct futex_h
WARN_ON(!atomic_read(&pi_state->refcount));
atomic_inc(&pi_state->refcount);
- me->pi_state = pi_state;
+ *ps = pi_state;
return 0;
}
@@ -516,7 +545,7 @@ lookup_pi_state(u32 uval, struct futex_h
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
/* Store the key for possible exit cleanups: */
- pi_state->key = me->key;
+ pi_state->key = *key;
spin_lock_irq(&p->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
@@ -526,7 +555,7 @@ lookup_pi_state(u32 uval, struct futex_h
put_task_struct(p);
- me->pi_state = pi_state;
+ *ps = pi_state;
return 0;
}
@@ -563,11 +592,12 @@ static int wake_futex_pi(u32 __user *uad
struct task_struct *new_owner;
struct futex_pi_state *pi_state = this->pi_state;
u32 curval, newval;
+ unsigned long flags;
if (!pi_state)
return -EINVAL;
- spin_lock(&pi_state->pi_mutex.wait_lock);
+ spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
/*
@@ -586,28 +616,40 @@ static int wake_futex_pi(u32 __user *uad
*/
if (!(uval & FUTEX_OWNER_DIED)) {
newval = FUTEX_WAITERS | new_owner->pid;
+ /* Keep the FUTEX_WAITER_REQUEUED flag if it was set */
+ newval |= (uval & FUTEX_WAITER_REQUEUED);
inc_preempt_count();
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
dec_preempt_count();
- if (curval == -EFAULT)
+ if (curval == -EFAULT) {
+ spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock,
+ flags);
return -EFAULT;
- if (curval != uval)
+ }
+ if (curval != uval) {
+ spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock,
+ flags);
return -EINVAL;
+ }
+
+ if (uval & FUTEX_WAITER_REQUEUED)
+ rt_mutex_deadlock_account_lock(&pi_state->pi_mutex,
+ new_owner);
}
- spin_lock_irq(&pi_state->owner->pi_lock);
+ spin_lock(&pi_state->owner->pi_lock);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
- spin_unlock_irq(&pi_state->owner->pi_lock);
+ spin_unlock(&pi_state->owner->pi_lock);
- spin_lock_irq(&new_owner->pi_lock);
+ spin_lock(&new_owner->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &new_owner->pi_state_list);
pi_state->owner = new_owner;
- spin_unlock_irq(&new_owner->pi_lock);
+ spin_unlock(&new_owner->pi_lock);
+ spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
- spin_unlock(&pi_state->pi_mutex.wait_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
return 0;
@@ -650,6 +692,253 @@ double_lock_hb(struct futex_hash_bucket
}
/*
+ * Called from futex_requeue_pi.
+ * Set FUTEX_WAITERS and FUTEX_WAITER_REQUEUED flags on the
+ * PI-futex value; search its associated pi_state if an owner exist
+ * or create a new one without owner.
+ */
+static inline int lookup_pi_state_for_requeue(u32 __user *uaddr,
+ struct futex_hash_bucket *hb,
+ union futex_key *key,
+ struct futex_pi_state **pi_state)
+
+{
+ u32 curval, uval, newval;
+
+retry:
+ /*
+ * We can't handle a fault cleanly because we can't
+ * release the locks here. Simply return the fault.
+ */
+ if (get_futex_value_locked(&curval, uaddr))
+ return -EFAULT;
+
+ /* set the flags FUTEX_WAITERS and FUTEX_WAITER_REQUEUED */
+ if ((curval & (FUTEX_WAITERS | FUTEX_WAITER_REQUEUED))
+ != (FUTEX_WAITERS | FUTEX_WAITER_REQUEUED)) {
+ /*
+ * No waiters yet, we prepare the futex to have some waiters.
+ */
+
+ uval = curval;
+ newval = uval | FUTEX_WAITERS | FUTEX_WAITER_REQUEUED;
+
+ inc_preempt_count();
+ curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
+ dec_preempt_count();
+
+ if (unlikely(curval == -EFAULT))
+ return -EFAULT;
+ if (unlikely(curval != uval))
+ goto retry;
+ }
+
+ if (!(curval & FUTEX_TID_MASK)
+ || lookup_pi_state(curval, hb, key, pi_state)) {
+ /* the futex has no owner (yet) or the lookup failed:
+ allocate one pi_state without owner */
+
+ *pi_state = alloc_pi_state();
+
+ /* Already stores the key: */
+ (*pi_state)->key = *key;
+
+ /* init the mutex without owner */
+ __rt_mutex_init(&(*pi_state)->pi_mutex, NULL);
+ }
+
+ return 0;
+}
+
+/*
+ * Keep the first nr_wake waiter from futex1, wake up one,
+ * and requeue the next nr_requeue waiters following hashed on
+ * one physical page to another physical page (PI-futex uaddr2)
+ */
+static int futex_requeue_pi(u32 __user *uaddr1, u32 __user *uaddr2,
+ int nr_wake, int nr_requeue, u32 *cmpval)
+{
+ union futex_key key1, key2;
+ struct futex_hash_bucket *hb1, *hb2;
+ struct plist_head *head1;
+ struct futex_q *this, *next;
+ struct futex_pi_state *pi_state2 = NULL;
+ struct rt_mutex_waiter *waiter, *top_waiter = NULL;
+ struct rt_mutex *lock2 = NULL;
+ int ret, drop_count = 0;
+ unsigned long flags = 0;
+
+ if (refill_pi_state_cache())
+ return -ENOMEM;
+
+retry:
+ /*
+ * First take all the futex related locks:
+ */
+ down_read(¤t->mm->mmap_sem);
+
+ ret = get_futex_key(uaddr1, &key1);
+ if (unlikely(ret != 0))
+ goto out;
+ ret = get_futex_key(uaddr2, &key2);
+ if (unlikely(ret != 0))
+ goto out;
+
+ hb1 = hash_futex(&key1);
+ hb2 = hash_futex(&key2);
+
+ double_lock_hb(hb1, hb2);
+
+ if (likely(cmpval != NULL)) {
+ u32 curval;
+
+ ret = get_futex_value_locked(&curval, uaddr1);
+
+ if (unlikely(ret)) {
+ spin_unlock(&hb1->lock);
+ if (hb1 != hb2)
+ spin_unlock(&hb2->lock);
+
+ /*
+ * If we would have faulted, release mmap_sem, fault
+ * it in and start all over again.
+ */
+ up_read(¤t->mm->mmap_sem);
+
+ ret = get_user(curval, uaddr1);
+
+ if (!ret)
+ goto retry;
+
+ return ret;
+ }
+ if (curval != *cmpval) {
+ ret = -EAGAIN;
+ 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 {
+ /*
+ * FIRST: get and set the pi_state
+ */
+ if (!pi_state2) {
+ int s;
+ /* do this only the first time we requeue someone */
+ s = lookup_pi_state_for_requeue(uaddr2, hb2,
+ &key2, &pi_state2);
+ if (s) {
+ ret = s;
+ goto out_unlock;
+ }
+
+ lock2 = &pi_state2->pi_mutex;
+ spin_lock_irqsave(&lock2->wait_lock, flags);
+
+ /* Save the top waiter of the wait_list */
+ if (rt_mutex_has_waiters(lock2))
+ top_waiter = rt_mutex_top_waiter(lock2);
+ } else
+ atomic_inc(&pi_state2->refcount);
+
+
+ this->pi_state = pi_state2;
+
+ /*
+ * SECOND: requeue futex_q to the correct hashbucket
+ */
+
+ /*
+ * 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;
+ }
+ this->key = key2;
+ get_key_refs(&key2);
+ drop_count++;
+
+
+ /*
+ * THIRD: queue it to lock2
+ */
+ spin_lock(&this->task->pi_lock);
+ waiter = &this->waiter;
+ waiter->task = this->task;
+ waiter->lock = lock2;
+ plist_node_init(&waiter->list_entry, this->task->prio);
+ plist_node_init(&waiter->pi_list_entry, this->task->prio);
+ plist_add(&waiter->list_entry, &lock2->wait_list);
+ this->task->pi_blocked_on = waiter;
+ spin_unlock(&this->task->pi_lock);
+
+ if (ret - nr_wake >= nr_requeue)
+ break;
+ }
+ }
+
+ /* If we've requeued some tasks and the top_waiter of the rt_mutex
+ has changed, we must adjust the priority of the owner, if any */
+ if (drop_count) {
+ struct task_struct *owner = rt_mutex_owner(lock2);
+ if (owner &&
+ (top_waiter != (waiter = rt_mutex_top_waiter(lock2)))) {
+ int chain_walk = 0;
+
+ spin_lock(&owner->pi_lock);
+ if (top_waiter)
+ plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
+ else
+ /*
+ * There was no waiters before the requeue,
+ * the flag must be updated
+ */
+ mark_rt_mutex_waiters(lock2);
+
+ plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
+ __rt_mutex_adjust_prio(owner);
+ if (owner->pi_blocked_on) {
+ chain_walk = 1;
+ get_task_struct(owner);
+ }
+
+ spin_unlock(&owner->pi_lock);
+ spin_unlock_irqrestore(&lock2->wait_lock, flags);
+
+ if (chain_walk)
+ rt_mutex_adjust_prio_chain(owner, 0, lock2, NULL,
+ current);
+ } else {
+ /* No owner or the top_waiter does not change */
+ mark_rt_mutex_waiters(lock2);
+ spin_unlock_irqrestore(&lock2->wait_lock, flags);
+ }
+ }
+
+out_unlock:
+ spin_unlock(&hb1->lock);
+ if (hb1 != hb2)
+ spin_unlock(&hb2->lock);
+
+ /* drop_key_refs() must be called outside the spinlocks. */
+ while (--drop_count >= 0)
+ drop_key_refs(&key1);
+
+out:
+ up_read(¤t->mm->mmap_sem);
+ return ret;
+}
+
+/*
* Wake up all waiters hashed on the physical page that is mapped
* to this virtual address:
*/
@@ -990,9 +1279,10 @@ static int unqueue_me(struct futex_q *q)
/*
* PI futexes can not be requeued and must remove themself from the
- * hash bucket. The hash bucket lock is held on entry and dropped here.
+ * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
+ * and dropped here.
*/
-static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
+static void unqueue_me_pi(struct futex_q *q)
{
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
@@ -1001,11 +1291,65 @@ static void unqueue_me_pi(struct futex_q
free_pi_state(q->pi_state);
q->pi_state = NULL;
- spin_unlock(&hb->lock);
+ spin_unlock(q->lock_ptr);
drop_key_refs(&q->key);
}
+/*
+ * Fixup the pi_state owner with current.
+ *
+ * The cur->mm semaphore must be held, it is released at return of this
+ * function.
+ */
+static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ struct futex_hash_bucket *hb,
+ struct task_struct *curr)
+{
+ u32 newtid = curr->pid | FUTEX_WAITERS;
+ struct futex_pi_state *pi_state = q->pi_state;
+ u32 uval, curval, newval;
+ int ret;
+
+ /* Owner died? */
+ if (pi_state->owner != NULL) {
+ spin_lock_irq(&pi_state->owner->pi_lock);
+ WARN_ON(list_empty(&pi_state->list));
+ list_del_init(&pi_state->list);
+ spin_unlock_irq(&pi_state->owner->pi_lock);
+ } else
+ newtid |= FUTEX_OWNER_DIED;
+
+ pi_state->owner = curr;
+
+ spin_lock_irq(&curr->pi_lock);
+ WARN_ON(!list_empty(&pi_state->list));
+ list_add(&pi_state->list, &curr->pi_state_list);
+ spin_unlock_irq(&curr->pi_lock);
+
+ /* Unqueue and drop the lock */
+ unqueue_me_pi(q);
+ up_read(&curr->mm->mmap_sem);
+ /*
+ * We own it, so we have to replace the pending owner
+ * TID. This must be atomic as we have preserve the
+ * owner died bit here.
+ */
+ ret = get_user(uval, uaddr);
+ while (!ret) {
+ newval = (uval & FUTEX_OWNER_DIED) | newtid;
+ newval |= (uval & FUTEX_WAITER_REQUEUED);
+ curval = futex_atomic_cmpxchg_inatomic(uaddr,
+ uval, newval);
+ if (curval == -EFAULT)
+ ret = -EFAULT;
+ if (curval == uval)
+ break;
+ uval = curval;
+ }
+ return ret;
+}
+
static int futex_wait(u32 __user *uaddr, u32 val, struct timespec *time)
{
struct task_struct *curr = current;
@@ -1014,7 +1358,7 @@ static int futex_wait(u32 __user *uaddr,
struct futex_q q;
u32 uval;
int ret;
- struct hrtimer_sleeper t;
+ struct hrtimer_sleeper t, *to = NULL;
int rem = 0;
q.pi_state = NULL;
@@ -1068,6 +1412,14 @@ static int futex_wait(u32 __user *uaddr,
if (uval != val)
goto out_unlock_release_sem;
+ /*
+ * This rt_mutex_waiter structure is prepared here and will
+ * be used only if this task is requeued from a normal futex to
+ * a PI-futex with futex_requeue_pi.
+ */
+ debug_rt_mutex_init_waiter(&q.waiter);
+ q.waiter.task = NULL;
+
/* Only actually queue if *uaddr contained val. */
__queue_me(&q, hb);
@@ -1101,7 +1453,7 @@ static int futex_wait(u32 __user *uaddr,
if (time->tv_sec == 0 && time->tv_nsec == 0)
schedule();
else {
-
+ to = &t;
hrtimer_init(&t.timer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
hrtimer_init_sleeper(&t, current);
@@ -1133,6 +1485,67 @@ static int futex_wait(u32 __user *uaddr,
* we are the only user of it.
*/
+ if (q.pi_state) {
+ /*
+ * We were woken but have been requeued on a PI-futex.
+ * We have to complete the lock acquisition by taking
+ * the rtmutex.
+ */
+
+ struct rt_mutex *lock = &q.pi_state->pi_mutex;
+ unsigned long flags;
+
+ spin_lock_irqsave(&lock->wait_lock, flags);
+ if (unlikely(q.waiter.task)) {
+ remove_waiter(lock, &q.waiter, flags);
+ }
+ spin_unlock_irqrestore(&lock->wait_lock, flags);
+
+ if (rem)
+ ret = -ETIMEDOUT;
+ else
+ ret = rt_mutex_timed_lock(lock, to, 1);
+
+ down_read(&curr->mm->mmap_sem);
+ spin_lock(q.lock_ptr);
+
+ /*
+ * 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 (!ret && q.pi_state->owner != curr) {
+ /*
+ * We MUST play with the futex we were requeued on,
+ * NOT the current futex.
+ * We can retrieve it from the key of the pi_state
+ */
+ uaddr = get_futex_address(&q.pi_state->key);
+
+ /* mmap_sem and hash_bucket lock are unlocked at
+ return of this function */
+ ret = fixup_pi_state_owner(uaddr, &q, hb, curr);
+ } else {
+ /*
+ * Catch the rare case, where the lock was released
+ * when we were on the way back before we locked
+ * the hash bucket.
+ */
+ if (ret && q.pi_state->owner == curr) {
+ if (rt_mutex_trylock(&q.pi_state->pi_mutex))
+ ret = 0;
+ }
+ /* Unqueue and drop the lock */
+ unqueue_me_pi(&q);
+ up_read(&curr->mm->mmap_sem);
+ }
+
+ debug_rt_mutex_free_waiter(&q.waiter);
+
+ return ret;
+ }
+
+ debug_rt_mutex_free_waiter(&q.waiter);
+
/* If we were woken (and unqueued), we succeeded, whatever. */
if (!unqueue_me(&q))
return 0;
@@ -1152,6 +1565,52 @@ static int futex_wait(u32 __user *uaddr,
return ret;
}
+static void set_pi_futex_owner(struct futex_hash_bucket *hb,
+ union futex_key *key, struct task_struct *p)
+{
+ struct plist_head *head;
+ struct futex_q *this, *next;
+ struct futex_pi_state *pi_state = NULL;
+ struct rt_mutex *lock;
+ unsigned long flags;
+
+ /* Search a waiter that should already exists */
+
+ head = &hb->chain;
+
+ plist_for_each_entry_safe(this, next, head, list) {
+ if (match_futex (&this->key, key)) {
+ pi_state = this->pi_state;
+ break;
+ }
+ }
+
+ BUG_ON(!pi_state);
+
+ /* set p as pi_state's owner */
+ atomic_inc(&pi_state->refcount);
+
+ lock = &pi_state->pi_mutex;
+
+ spin_lock_irqsave(&lock->wait_lock, flags);
+ spin_lock(&p->pi_lock);
+
+ list_add(&pi_state->list, &p->pi_state_list);
+ pi_state->owner = p;
+
+ debug_rt_mutex_proxy_lock(lock, p);
+ WARN_ON(rt_mutex_owner(lock));
+ rt_mutex_set_owner(lock, p, 0);
+ rt_mutex_deadlock_account_lock(lock, p);
+
+ plist_add(&rt_mutex_top_waiter(lock)->pi_list_entry,
+ &p->pi_waiters);
+ __rt_mutex_adjust_prio(p);
+
+ spin_unlock(&p->pi_lock);
+ spin_unlock_irqrestore(&lock->wait_lock, flags);
+}
+
/*
* Userspace tried a 0 -> TID atomic transition of the futex value
* and failed. The kernel side here does the whole locking operation:
@@ -1166,7 +1625,7 @@ static int futex_lock_pi(u32 __user *uad
struct futex_hash_bucket *hb;
u32 uval, newval, curval;
struct futex_q q;
- int ret, attempt = 0;
+ int ret, lock_held, attempt = 0;
if (refill_pi_state_cache())
return -ENOMEM;
@@ -1189,6 +1648,8 @@ static int futex_lock_pi(u32 __user *uad
hb = queue_lock(&q, -1, NULL);
retry_locked:
+ lock_held = 0;
+
/*
* To avoid races, we attempt to take the lock here again
* (by doing a 0 -> TID atomic cmpxchg), while holding all
@@ -1207,7 +1668,16 @@ static int futex_lock_pi(u32 __user *uad
if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
if (!detect && 0)
force_sig(SIGKILL, current);
- ret = -EDEADLK;
+ /*
+ * Normally, this check is done in user space.
+ * In case of requeue, the owner may attempt to lock this futex,
+ * even if the ownership has already been given by the previous
+ * waker.
+ * In the usual case, this is a case of deadlock, but not in case
+ * of REQUEUE_PI.
+ */
+ if (!(curval & FUTEX_WAITER_REQUEUED))
+ ret = -EDEADLK;
goto out_unlock_release_sem;
}
@@ -1219,7 +1689,18 @@ static int futex_lock_pi(u32 __user *uad
goto out_unlock_release_sem;
uval = curval;
- newval = uval | FUTEX_WAITERS;
+ /*
+ * In case of a requeue, check if there already is an owner
+ * If not, just take the futex.
+ */
+ if ((curval & FUTEX_WAITER_REQUEUED) && !(curval & FUTEX_TID_MASK)) {
+ /* set current as futex owner */
+ newval = curval | current->pid;
+ lock_held = 1;
+ } else
+ /* Set the WAITERS flag, so the owner will know it has someone
+ to wake at next unlock */
+ newval = curval | FUTEX_WAITERS;
inc_preempt_count();
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
@@ -1230,11 +1711,16 @@ static int futex_lock_pi(u32 __user *uad
if (unlikely(curval != uval))
goto retry_locked;
+ if (lock_held) {
+ set_pi_futex_owner(hb, &q.key, curr);
+ goto out_unlock_release_sem;
+ }
+
/*
* 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);
+ ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
if (unlikely(ret)) {
/*
@@ -1297,45 +1783,10 @@ static int futex_lock_pi(u32 __user *uad
* 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 (!ret && q.pi_state->owner != curr) {
- u32 newtid = current->pid | FUTEX_WAITERS;
-
- /* Owner died? */
- if (q.pi_state->owner != NULL) {
- spin_lock_irq(&q.pi_state->owner->pi_lock);
- WARN_ON(list_empty(&q.pi_state->list));
- list_del_init(&q.pi_state->list);
- spin_unlock_irq(&q.pi_state->owner->pi_lock);
- } else
- newtid |= FUTEX_OWNER_DIED;
-
- q.pi_state->owner = current;
-
- spin_lock_irq(¤t->pi_lock);
- WARN_ON(!list_empty(&q.pi_state->list));
- list_add(&q.pi_state->list, ¤t->pi_state_list);
- spin_unlock_irq(¤t->pi_lock);
-
- /* Unqueue and drop the lock */
- unqueue_me_pi(&q, hb);
- up_read(&curr->mm->mmap_sem);
- /*
- * We own it, so we have to replace the pending owner
- * TID. This must be atomic as we have preserve the
- * owner died bit here.
- */
- ret = get_user(uval, uaddr);
- while (!ret) {
- newval = (uval & FUTEX_OWNER_DIED) | newtid;
- curval = futex_atomic_cmpxchg_inatomic(uaddr,
- uval, newval);
- if (curval == -EFAULT)
- ret = -EFAULT;
- if (curval == uval)
- break;
- uval = curval;
- }
- } else {
+ if (!ret && q.pi_state->owner != curr)
+ /* mmap_sem is unlocked at return of this function */
+ ret = fixup_pi_state_owner(uaddr, &q, hb, curr);
+ else {
/*
* Catch the rare case, where the lock was released
* when we were on the way back before we locked
@@ -1346,7 +1797,7 @@ static int futex_lock_pi(u32 __user *uad
ret = 0;
}
/* Unqueue and drop the lock */
- unqueue_me_pi(&q, hb);
+ unqueue_me_pi(&q);
up_read(&curr->mm->mmap_sem);
}
@@ -1715,6 +2166,8 @@ retry:
* userspace.
*/
mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
+ /* Also keep the FUTEX_WAITER_REQUEUED flag if set */
+ mval |= (uval & FUTEX_WAITER_REQUEUED);
nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
if (nval == -EFAULT)
@@ -1845,6 +2298,9 @@ long do_futex(u32 __user *uaddr, int op,
case FUTEX_TRYLOCK_PI:
ret = futex_lock_pi(uaddr, 0, timeout, 1);
break;
+ case FUTEX_CMP_REQUEUE_PI:
+ ret = futex_requeue_pi(uaddr, uaddr2, val, val2, &val3);
+ break;
default:
ret = -ENOSYS;
}
@@ -2745,7 +3201,8 @@ asmlinkage long sys_futex(u32 __user *ua
/*
* requeue parameter in 'utime' if op == FUTEX_REQUEUE.
*/
- if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
+ if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE
+ || op == FUTEX_CMP_REQUEUE_PI)
val2 = (u32) (unsigned long) utime;
return do_futex(uaddr, op, val, &t, uaddr2, val2, val3);
Index: linux-2.6/kernel/rtmutex.c
===================================================================
--- linux-2.6.orig/kernel/rtmutex.c 2006-12-12 16:38:00.000000000 +0100
+++ linux-2.6/kernel/rtmutex.c 2006-12-12 16:44:17.000000000 +0100
@@ -56,7 +56,7 @@
* state.
*/
-static void
+void
rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
unsigned long mask)
{
@@ -80,29 +80,6 @@ static void fixup_rt_mutex_waiters(struc
clear_rt_mutex_waiters(lock);
}
-/*
- * We can speed up the acquire/release, if the architecture
- * supports cmpxchg and if there's no debugging state to be set up
- */
-#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
-# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
-static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
-{
- unsigned long owner, *p = (unsigned long *) &lock->owner;
-
- do {
- owner = *p;
- cpu_relax();
- } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
-}
-#else
-# define rt_mutex_cmpxchg(l,c,n) (0)
-static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
-{
- lock->owner = (struct task_struct *)
- ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
-}
-#endif
int pi_initialized;
@@ -140,7 +117,7 @@ int rt_mutex_getprio(struct task_struct
*
* This can be both boosting and unboosting. task->pi_lock must be held.
*/
-static void __rt_mutex_adjust_prio(struct task_struct *task)
+void __rt_mutex_adjust_prio(struct task_struct *task)
{
int prio = rt_mutex_getprio(task);
@@ -176,11 +153,11 @@ int max_lock_depth = 1024;
* Decreases task's usage by one - may thus free the task.
* Returns 0 or -EDEADLK.
*/
-static int rt_mutex_adjust_prio_chain(struct task_struct *task,
- int deadlock_detect,
- struct rt_mutex *orig_lock,
- struct rt_mutex_waiter *orig_waiter,
- struct task_struct *top_task)
+int rt_mutex_adjust_prio_chain(struct task_struct *task,
+ int deadlock_detect,
+ struct rt_mutex *orig_lock,
+ struct rt_mutex_waiter *orig_waiter,
+ struct task_struct *top_task)
{
struct rt_mutex *lock;
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
@@ -541,9 +518,9 @@ static void wakeup_next_waiter(struct rt
*
* Must be called with lock->wait_lock held
*/
-static void remove_waiter(struct rt_mutex *lock,
- struct rt_mutex_waiter *waiter,
- unsigned long flags)
+void remove_waiter(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ unsigned long flags)
{
int first = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
Index: linux-2.6/kernel/rtmutex_common.h
===================================================================
--- linux-2.6.orig/kernel/rtmutex_common.h 2006-12-12 16:38:00.000000000 +0100
+++ linux-2.6/kernel/rtmutex_common.h 2006-12-12 16:43:54.000000000 +0100
@@ -113,6 +113,30 @@ static inline unsigned long rt_mutex_own
}
/*
+ * We can speed up the acquire/release, if the architecture
+ * supports cmpxchg and if there's no debugging state to be set up
+ */
+#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
+# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
+static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
+{
+ unsigned long owner, *p = (unsigned long *) &lock->owner;
+
+ do {
+ owner = *p;
+ cpu_relax();
+ } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
+}
+#else
+# define rt_mutex_cmpxchg(l,c,n) (0)
+static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
+{
+ lock->owner = (struct task_struct *)
+ ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
+}
+#endif
+
+/*
* PI-futex support (proxy locking functions, etc.):
*/
extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
@@ -120,4 +144,16 @@ extern void rt_mutex_init_proxy_locked(s
struct task_struct *proxy_owner);
extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
struct task_struct *proxy_owner);
+
+extern void rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
+ unsigned long mask);
+extern void __rt_mutex_adjust_prio(struct task_struct *task);
+extern int rt_mutex_adjust_prio_chain(struct task_struct *task,
+ int deadlock_detect,
+ struct rt_mutex *orig_lock,
+ struct rt_mutex_waiter *orig_waiter,
+ struct task_struct *top_task);
+extern void remove_waiter(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ unsigned long flags);
#endif
Index: linux-2.6/kernel/futex_compat.c
===================================================================
--- linux-2.6.orig/kernel/futex_compat.c 2006-12-12 16:38:00.000000000 +0100
+++ linux-2.6/kernel/futex_compat.c 2006-12-12 16:43:54.000000000 +0100
@@ -150,7 +150,8 @@ asmlinkage long compat_sys_futex(u32 __u
if (!timespec_valid(&t))
return -EINVAL;
}
- if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
+ if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE
+ || op == FUTEX_CMP_REQUEUE_PI)
val2 = (int) (unsigned long) utime;
return do_futex(uaddr, op, val, &t, uaddr2, val2, val3);
Thanks,
--
Pierre Peiffer
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