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Subject[git pull] core kernel fixes
Linus,

please pull the latest core kernel fixes git tree from:

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

Ingo

------------------>
Thomas Gleixner (1):
futexes: fix fault handling in futex_lock_pi

kernel/futex.c | 93 ++++++++++++++++++++++++++++++++++++++++++++------------
1 files changed, 73 insertions(+), 20 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 449def8..7d1136e 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1096,21 +1096,64 @@ static void unqueue_me_pi(struct futex_q *q)
* private futexes.
*/
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *newowner)
+ struct task_struct *newowner,
+ struct rw_semaphore *fshared)
{
u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
struct futex_pi_state *pi_state = q->pi_state;
+ struct task_struct *oldowner = pi_state->owner;
u32 uval, curval, newval;
- int ret;
+ int ret, attempt = 0;

/* Owner died? */
+ if (!pi_state->owner)
+ newtid |= FUTEX_OWNER_DIED;
+
+ /*
+ * We are here either because we stole the rtmutex from the
+ * pending owner or we are the pending owner which failed to
+ * get the rtmutex. We have to replace the pending owner TID
+ * 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.
+ *
+ * Modifying pi_state _before_ the user space value would
+ * leave the pi_state in an inconsistent state when we fault
+ * here, because we need to drop the hash bucket lock to
+ * handle the fault. This might be observed in the PID check
+ * in lookup_pi_state.
+ */
+retry:
+ if (get_futex_value_locked(&uval, uaddr))
+ goto handle_fault;
+
+ while (1) {
+ newval = (uval & FUTEX_OWNER_DIED) | newtid;
+
+ curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
+
+ if (curval == -EFAULT)
+ goto handle_fault;
+ if (curval == uval)
+ break;
+ uval = curval;
+ }
+
+ /*
+ * We fixed up user space. Now we need to fix the pi_state
+ * itself.
+ */
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 = newowner;

@@ -1118,26 +1161,35 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &newowner->pi_state_list);
spin_unlock_irq(&newowner->pi_lock);
+ return 0;

/*
- * 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.
+ * To handle the page fault we need to drop the hash bucket
+ * lock here. That gives the other task (either the pending
+ * owner itself or the task which stole the rtmutex) the
+ * chance to try the fixup of the pi_state. So once we are
+ * back from handling the fault we need to check the pi_state
+ * after reacquiring the hash bucket lock and before trying to
+ * do another fixup. When the fixup has been done already we
+ * simply return.
*/
- ret = get_futex_value_locked(&uval, uaddr);
+handle_fault:
+ spin_unlock(q->lock_ptr);

- while (!ret) {
- newval = (uval & FUTEX_OWNER_DIED) | newtid;
+ ret = futex_handle_fault((unsigned long)uaddr, fshared, attempt++);

- curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
+ spin_lock(q->lock_ptr);

- if (curval == -EFAULT)
- ret = -EFAULT;
- if (curval == uval)
- break;
- uval = curval;
- }
- return ret;
+ /*
+ * Check if someone else fixed it for us:
+ */
+ if (pi_state->owner != oldowner)
+ return 0;
+
+ if (ret)
+ return ret;
+
+ goto retry;
}

/*
@@ -1507,7 +1559,7 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
* that case:
*/
if (q.pi_state->owner != curr)
- ret = fixup_pi_state_owner(uaddr, &q, curr);
+ ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
} else {
/*
* Catch the rare case, where the lock was released
@@ -1539,7 +1591,8 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
int res;

owner = rt_mutex_owner(&q.pi_state->pi_mutex);
- res = fixup_pi_state_owner(uaddr, &q, owner);
+ res = fixup_pi_state_owner(uaddr, &q, owner,
+ fshared);

/* propagate -EFAULT, if the fixup failed */
if (res)

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