[GIT PULL] futex updates for v2.6.30

From: Ingo Molnar
Date: Sat Mar 28 2009 - 18:29:23 EST

Linus,

Please pull the latest futexes-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git futexes-for-linus

Thanks,

Ingo

------------------>
Darren Hart (7):
futex: update futex commentary
futex: additional (get|put)_futex_key() fixes
futex: add double_unlock_hb()
futex: use current->time_slack_ns for rt tasks too
futex: unlock before returning -EFAULT
futex: clean up fault logic
futex: remove the pointer math from double_unlock_hb

Ingo Molnar (1):
futex: remove the pointer math from double_unlock_hb, fix


kernel/futex.c | 201 +++++++++++++++++++++-----------------------------------
1 files changed, 76 insertions(+), 125 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 438701a..6b50a02 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -114,7 +114,9 @@ struct futex_q {
};

/*
- * Split the global futex_lock into every hash list lock.
+ * Hash buckets are shared by all the futex_keys that hash to the same
+ * location. Each key may have multiple futex_q structures, one for each task
+ * waiting on a futex.
*/
struct futex_hash_bucket {
spinlock_t lock;
@@ -189,8 +191,7 @@ static void drop_futex_key_refs(union futex_key *key)
/**
* get_futex_key - Get parameters which are the keys for a futex.
* @uaddr: virtual address of the futex
- * @shared: NULL for a PROCESS_PRIVATE futex,
- * &current->mm->mmap_sem for a PROCESS_SHARED futex
+ * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
* @key: address where result is stored.
*
* Returns a negative error code or 0
@@ -200,9 +201,7 @@ static void drop_futex_key_refs(union futex_key *key)
* offset_within_page). For private mappings, it's (uaddr, current->mm).
* We can usually work out the index without swapping in the page.
*
- * fshared is NULL for PROCESS_PRIVATE futexes
- * For other futexes, it points to &current->mm->mmap_sem and
- * caller must have taken the reader lock. but NOT any spinlocks.
+ * lock_page() might sleep, the caller should not hold a spinlock.
*/
static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
{
@@ -299,41 +298,6 @@ static int get_futex_value_locked(u32 *dest, u32 __user *from)
return ret ? -EFAULT : 0;
}

-/*
- * Fault handling.
- */
-static int futex_handle_fault(unsigned long address, int attempt)
-{
- struct vm_area_struct * vma;
- struct mm_struct *mm = current->mm;
- int ret = -EFAULT;
-
- if (attempt > 2)
- return ret;
-
- down_read(&mm->mmap_sem);
- vma = find_vma(mm, address);
- if (vma && address >= vma->vm_start &&
- (vma->vm_flags & VM_WRITE)) {
- int fault;
- fault = handle_mm_fault(mm, vma, address, 1);
- if (unlikely((fault & VM_FAULT_ERROR))) {
-#if 0
- /* XXX: let's do this when we verify it is OK */
- if (ret & VM_FAULT_OOM)
- ret = -ENOMEM;
-#endif
- } else {
- ret = 0;
- if (fault & VM_FAULT_MAJOR)
- current->maj_flt++;
- else
- current->min_flt++;
- }
- }
- up_read(&mm->mmap_sem);
- return ret;
-}

/*
* PI code:
@@ -589,10 +553,9 @@ static void wake_futex(struct futex_q *q)
* 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_all() does not prevent this store from
- * moving.
+ * 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.
*/
smp_wmb();
q->lock_ptr = NULL;
@@ -692,9 +655,16 @@ double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
}
}

+static inline void
+double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+{
+ spin_unlock(&hb1->lock);
+ if (hb1 != hb2)
+ spin_unlock(&hb2->lock);
+}
+
/*
- * Wake up all waiters hashed on the physical page that is mapped
- * to this virtual address:
+ * Wake up waiters matching bitset queued on this futex (uaddr).
*/
static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
{
@@ -750,9 +720,9 @@ futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
struct futex_hash_bucket *hb1, *hb2;
struct plist_head *head;
struct futex_q *this, *next;
- int ret, op_ret, attempt = 0;
+ int ret, op_ret;

-retryfull:
+retry:
ret = get_futex_key(uaddr1, fshared, &key1);
if (unlikely(ret != 0))
goto out;
@@ -763,16 +733,13 @@ retryfull:
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);

-retry:
double_lock_hb(hb1, hb2);
-
+retry_private:
op_ret = futex_atomic_op_inuser(op, uaddr2);
if (unlikely(op_ret < 0)) {
u32 dummy;

- spin_unlock(&hb1->lock);
- if (hb1 != hb2)
- spin_unlock(&hb2->lock);
+ double_unlock_hb(hb1, hb2);

#ifndef CONFIG_MMU
/*
@@ -788,26 +755,16 @@ retry:
goto out_put_keys;
}

- /*
- * futex_atomic_op_inuser needs to both read and write
- * *(int __user *)uaddr2, but we can't modify it
- * non-atomically. Therefore, if get_user below is not
- * enough, we need to handle the fault ourselves, while
- * still holding the mmap_sem.
- */
- if (attempt++) {
- ret = futex_handle_fault((unsigned long)uaddr2,
- attempt);
- if (ret)
- goto out_put_keys;
- goto retry;
- }
-
ret = get_user(dummy, uaddr2);
if (ret)
- return ret;
+ goto out_put_keys;
+
+ if (!fshared)
+ goto retry_private;

- goto retryfull;
+ put_futex_key(fshared, &key2);
+ put_futex_key(fshared, &key1);
+ goto retry;
}

head = &hb1->chain;
@@ -834,9 +791,7 @@ retry:
ret += op_ret;
}

- spin_unlock(&hb1->lock);
- if (hb1 != hb2)
- spin_unlock(&hb2->lock);
+ double_unlock_hb(hb1, hb2);
out_put_keys:
put_futex_key(fshared, &key2);
out_put_key1:
@@ -869,6 +824,7 @@ retry:
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);

+retry_private:
double_lock_hb(hb1, hb2);

if (likely(cmpval != NULL)) {
@@ -877,16 +833,18 @@ retry:
ret = get_futex_value_locked(&curval, uaddr1);

if (unlikely(ret)) {
- spin_unlock(&hb1->lock);
- if (hb1 != hb2)
- spin_unlock(&hb2->lock);
+ double_unlock_hb(hb1, hb2);

ret = get_user(curval, uaddr1);
+ if (ret)
+ goto out_put_keys;

- if (!ret)
- goto retry;
+ if (!fshared)
+ goto retry_private;

- goto out_put_keys;
+ put_futex_key(fshared, &key2);
+ put_futex_key(fshared, &key1);
+ goto retry;
}
if (curval != *cmpval) {
ret = -EAGAIN;
@@ -923,9 +881,7 @@ retry:
}

out_unlock:
- spin_unlock(&hb1->lock);
- if (hb1 != hb2)
- spin_unlock(&hb2->lock);
+ double_unlock_hb(hb1, hb2);

/* drop_futex_key_refs() must be called outside the spinlocks. */
while (--drop_count >= 0)
@@ -1063,7 +1019,7 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
struct futex_pi_state *pi_state = q->pi_state;
struct task_struct *oldowner = pi_state->owner;
u32 uval, curval, newval;
- int ret, attempt = 0;
+ int ret;

/* Owner died? */
if (!pi_state->owner)
@@ -1076,11 +1032,9 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
* in the user space variable. This must be atomic as we have
* to preserve the owner died bit here.
*
- * Note: We write the user space value _before_ changing the
- * pi_state because we can fault here. Imagine swapped out
- * pages or a fork, which was running right before we acquired
- * mmap_sem, that marked all the anonymous memory readonly for
- * cow.
+ * Note: We write the user space value _before_ changing the pi_state
+ * because we can fault here. Imagine swapped out pages or a fork
+ * that marked all the anonymous memory readonly for cow.
*
* Modifying pi_state _before_ the user space value would
* leave the pi_state in an inconsistent state when we fault
@@ -1136,7 +1090,7 @@ retry:
handle_fault:
spin_unlock(q->lock_ptr);

- ret = futex_handle_fault((unsigned long)uaddr, attempt++);
+ ret = get_user(uval, uaddr);

spin_lock(q->lock_ptr);

@@ -1185,10 +1139,11 @@ retry:
if (unlikely(ret != 0))
goto out;

+retry_private:
hb = queue_lock(&q);

/*
- * Access the page AFTER the futex is queued.
+ * Access the page AFTER the hash-bucket is locked.
* Order is important:
*
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
@@ -1204,20 +1159,23 @@ retry:
* 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
+ * For shared futexes, we hold the mmap semaphore, so the mapping
* cannot have changed since we looked it up in get_futex_key.
*/
ret = get_futex_value_locked(&uval, uaddr);

if (unlikely(ret)) {
queue_unlock(&q, hb);
- put_futex_key(fshared, &q.key);

ret = get_user(uval, uaddr);
+ if (ret)
+ goto out_put_key;

- if (!ret)
- goto retry;
- goto out;
+ if (!fshared)
+ goto retry_private;
+
+ put_futex_key(fshared, &q.key);
+ goto retry;
}
ret = -EWOULDBLOCK;
if (unlikely(uval != val)) {
@@ -1248,16 +1206,13 @@ retry:
if (!abs_time)
schedule();
else {
- unsigned long slack;
- slack = current->timer_slack_ns;
- if (rt_task(current))
- slack = 0;
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, slack);
+ hrtimer_set_expires_range_ns(&t.timer, *abs_time,
+ current->timer_slack_ns);

hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
if (!hrtimer_active(&t.timer))
@@ -1354,7 +1309,7 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
struct futex_hash_bucket *hb;
u32 uval, newval, curval;
struct futex_q q;
- int ret, lock_taken, ownerdied = 0, attempt = 0;
+ int ret, lock_taken, ownerdied = 0;

if (refill_pi_state_cache())
return -ENOMEM;
@@ -1374,7 +1329,7 @@ retry:
if (unlikely(ret != 0))
goto out;

-retry_unlocked:
+retry_private:
hb = queue_lock(&q);

retry_locked:
@@ -1458,6 +1413,7 @@ retry_locked:
* exit to complete.
*/
queue_unlock(&q, hb);
+ put_futex_key(fshared, &q.key);
cond_resched();
goto retry;

@@ -1564,6 +1520,13 @@ retry_locked:
}
}

+ /*
+ * If fixup_pi_state_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);
+
/* Unqueue and drop the lock */
unqueue_me_pi(&q);

@@ -1591,22 +1554,18 @@ uaddr_faulted:
*/
queue_unlock(&q, hb);

- if (attempt++) {
- ret = futex_handle_fault((unsigned long)uaddr, attempt);
- if (ret)
- goto out_put_key;
- goto retry_unlocked;
- }
-
ret = get_user(uval, uaddr);
- if (!ret)
- goto retry;
+ if (ret)
+ goto out_put_key;

- if (to)
- destroy_hrtimer_on_stack(&to->timer);
- return ret;
+ if (!fshared)
+ goto retry_private;
+
+ put_futex_key(fshared, &q.key);
+ goto retry;
}

+
/*
* Userspace attempted a TID -> 0 atomic transition, and failed.
* This is the in-kernel slowpath: we look up the PI state (if any),
@@ -1619,7 +1578,7 @@ static int futex_unlock_pi(u32 __user *uaddr, int fshared)
u32 uval;
struct plist_head *head;
union futex_key key = FUTEX_KEY_INIT;
- int ret, attempt = 0;
+ int ret;

retry:
if (get_user(uval, uaddr))
@@ -1635,7 +1594,6 @@ retry:
goto out;

hb = hash_futex(&key);
-retry_unlocked:
spin_lock(&hb->lock);

/*
@@ -1700,14 +1658,7 @@ pi_faulted:
* we have to drop the mmap_sem in order to call get_user().
*/
spin_unlock(&hb->lock);
-
- if (attempt++) {
- ret = futex_handle_fault((unsigned long)uaddr, attempt);
- if (ret)
- goto out;
- uval = 0;
- goto retry_unlocked;
- }
+ put_futex_key(fshared, &key);

ret = get_user(uval, uaddr);
if (!ret)
--
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