On Thu, Mar 17, 2005 at 03:20:31PM +0000, Jamie Lokier wrote:
> > [numerous instances of...]
> > + preempt_check_resched();
>
> Not required. The spin unlocks will do this.
Here is updated patch with those removed (all of them are preceeded
by spin_unlock) and out_unqueue label and following unused code removed
too.
--- linux-2.6.11/kernel/futex.c.jj 2005-03-17 04:42:29.000000000 -0500
+++ linux-2.6.11/kernel/futex.c 2005-03-18 05:45:29.000000000 -0500
@@ -97,7 +97,6 @@ struct futex_q {
*/
struct futex_hash_bucket {
spinlock_t lock;
- unsigned int nqueued;
struct list_head chain;
};
@@ -265,7 +264,6 @@ static inline int get_futex_value_locked
inc_preempt_count();
ret = __copy_from_user_inatomic(dest, from, sizeof(int));
dec_preempt_count();
- preempt_check_resched();
return ret ? -EFAULT : 0;
}
@@ -339,7 +337,6 @@ static int futex_requeue(unsigned long u
struct list_head *head1;
struct futex_q *this, *next;
int ret, drop_count = 0;
- unsigned int nqueued;
retry:
down_read(¤t->mm->mmap_sem);
@@ -354,23 +351,22 @@ static int futex_requeue(unsigned long u
bh1 = hash_futex(&key1);
bh2 = hash_futex(&key2);
- nqueued = bh1->nqueued;
+ if (bh1 < bh2)
+ spin_lock(&bh1->lock);
+ spin_lock(&bh2->lock);
+ if (bh1 > bh2)
+ spin_lock(&bh1->lock);
+
if (likely(valp != NULL)) {
int curval;
- /* In order to avoid doing get_user while
- holding bh1->lock and bh2->lock, nqueued
- (monotonically increasing field) must be first
- read, then *uaddr1 fetched from userland and
- after acquiring lock nqueued field compared with
- the stored value. The smp_mb () below
- makes sure that bh1->nqueued is read from memory
- before *uaddr1. */
- smp_mb();
-
ret = get_futex_value_locked(&curval, (int __user *)uaddr1);
if (unlikely(ret)) {
+ spin_unlock(&bh1->lock);
+ if (bh1 != bh2)
+ spin_unlock(&bh2->lock);
+
/* If we would have faulted, release mmap_sem, fault
* it in and start all over again.
*/
@@ -385,21 +381,10 @@ static int futex_requeue(unsigned long u
}
if (curval != *valp) {
ret = -EAGAIN;
- goto out;
+ goto out_unlock;
}
}
- if (bh1 < bh2)
- spin_lock(&bh1->lock);
- spin_lock(&bh2->lock);
- if (bh1 > bh2)
- spin_lock(&bh1->lock);
-
- if (unlikely(nqueued != bh1->nqueued && valp != NULL)) {
- ret = -EAGAIN;
- goto out_unlock;
- }
-
head1 = &bh1->chain;
list_for_each_entry_safe(this, next, head1, list) {
if (!match_futex (&this->key, &key1))
@@ -435,13 +420,9 @@ out:
return ret;
}
-/*
- * queue_me and unqueue_me must be called as a pair, each
- * exactly once. They are called with the hashed spinlock held.
- */
-
/* The key must be already stored in q->key. */
-static void queue_me(struct futex_q *q, int fd, struct file *filp)
+static inline struct futex_hash_bucket *
+queue_lock(struct futex_q *q, int fd, struct file *filp)
{
struct futex_hash_bucket *bh;
@@ -455,11 +436,35 @@ static void queue_me(struct futex_q *q,
q->lock_ptr = &bh->lock;
spin_lock(&bh->lock);
- bh->nqueued++;
+ return bh;
+}
+
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh)
+{
list_add_tail(&q->list, &bh->chain);
spin_unlock(&bh->lock);
}
+static inline void
+queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh)
+{
+ spin_unlock(&bh->lock);
+ drop_key_refs(&q->key);
+}
+
+/*
+ * queue_me and unqueue_me must be called as a pair, each
+ * exactly once. They are called with the hashed spinlock held.
+ */
+
+/* The key must be already stored in q->key. */
+static void queue_me(struct futex_q *q, int fd, struct file *filp)
+{
+ struct futex_hash_bucket *bh;
+ bh = queue_lock(q, fd, filp);
+ __queue_me(q, bh);
+}
+
/* Return 1 if we were still queued (ie. 0 means we were woken) */
static int unqueue_me(struct futex_q *q)
{
@@ -503,6 +508,7 @@ static int futex_wait(unsigned long uadd
DECLARE_WAITQUEUE(wait, current);
int ret, curval;
struct futex_q q;
+ struct futex_hash_bucket *bh;
retry:
down_read(¤t->mm->mmap_sem);
@@ -511,7 +517,7 @@ static int futex_wait(unsigned long uadd
if (unlikely(ret != 0))
goto out_release_sem;
- queue_me(&q, -1, NULL);
+ bh = queue_lock(&q, -1, NULL);
/*
* Access the page AFTER the futex is queued.
@@ -537,14 +543,13 @@ static int futex_wait(unsigned long uadd
ret = get_futex_value_locked(&curval, (int __user *)uaddr);
if (unlikely(ret)) {
+ queue_unlock(&q, bh);
+
/* If we would have faulted, release mmap_sem, fault it in and
* start all over again.
*/
up_read(¤t->mm->mmap_sem);
- if (!unqueue_me(&q)) /* There's a chance we got woken already */
- return 0;
-
ret = get_user(curval, (int __user *)uaddr);
if (!ret)
@@ -553,9 +558,13 @@ static int futex_wait(unsigned long uadd
}
if (curval != val) {
ret = -EWOULDBLOCK;
- goto out_unqueue;
+ queue_unlock(&q, bh);
+ goto out_release_sem;
}
+ /* Only actually queue if *uaddr contained val. */
+ __queue_me(&q, bh);
+
/*
* Now the futex is queued and we have checked the data, we
* don't want to hold mmap_sem while we sleep.
@@ -596,10 +605,6 @@ static int futex_wait(unsigned long uadd
* have handled it for us already. */
return -EINTR;
- out_unqueue:
- /* If we were woken (and unqueued), we succeeded, whatever. */
- if (!unqueue_me(&q))
- ret = 0;
out_release_sem:
up_read(¤t->mm->mmap_sem);
return ret;
Jakub
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