[PATCH] pi-futex: robust-futex exit crash fix

Fix pi_state->list handling bugs: list handling mishap, locking error.
Plus add more debug checks and fix a few style issues i noticed while
debugging this.

(reported by Ulrich Drepper and Jakub Jelinek.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 24 insertions, 8 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index cf0c8e21d1ab..f59003b1d8f9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -415,15 +415,15 @@ out_unlock:
  */
 void exit_pi_state_list(struct task_struct *curr)
 {
-        struct futex_hash_bucket *hb;
         struct list_head *next, *head = &curr->pi_state_list;
         struct futex_pi_state *pi_state;
+        struct futex_hash_bucket *hb;
         union futex_key key;
 
         /*
          * We are a ZOMBIE and nobody can enqueue itself on
          * pi_state_list anymore, but we have to be careful
-         * versus waiters unqueueing themselfs
+         * versus waiters unqueueing themselves:
          */
         spin_lock_irq(&curr->pi_lock);
         while (!list_empty(head)) {
@@ -431,21 +431,24 @@ void exit_pi_state_list(struct task_struct *curr)
                 next = head->next;
                 pi_state = list_entry(next, struct futex_pi_state, list);
                 key = pi_state->key;
+                hb = hash_futex(&key);
                 spin_unlock_irq(&curr->pi_lock);
 
-                hb = hash_futex(&key);
                 spin_lock(&hb->lock);
 
                 spin_lock_irq(&curr->pi_lock);
+                /*
+                 * We dropped the pi-lock, so re-check whether this
+                 * task still owns the PI-state:
+                 */
                 if (head->next != next) {
                         spin_unlock(&hb->lock);
                         continue;
                 }
 
-                list_del_init(&pi_state->list);
-
                 WARN_ON(pi_state->owner != curr);
-
+                WARN_ON(list_empty(&pi_state->list));
+                list_del_init(&pi_state->list);
                 pi_state->owner = NULL;
                 spin_unlock_irq(&curr->pi_lock);
 
@@ -470,7 +473,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
         head = &hb->chain;
 
         list_for_each_entry_safe(this, next, head, list) {
-                if (match_futex (&this->key, &me->key)) {
+                if (match_futex(&this->key, &me->key)) {
                         /*
                          * Another waiter already exists - bump up
                          * the refcount and return its pi_state:
@@ -482,6 +485,8 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
                         if (unlikely(!pi_state))
                                 return -EINVAL;
 
+                        WARN_ON(!atomic_read(&pi_state->refcount));
+
                         atomic_inc(&pi_state->refcount);
                         me->pi_state = pi_state;
 
@@ -510,6 +515,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
         pi_state->key = me->key;
 
         spin_lock_irq(&p->pi_lock);
+        WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &p->pi_state_list);
         pi_state->owner = p;
         spin_unlock_irq(&p->pi_lock);
@@ -584,9 +590,17 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
         if (curval != uval)
                 return -EINVAL;
 
-        list_del_init(&pi_state->owner->pi_state_list);
+        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);
+
+        spin_lock_irq(&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);
+
         rt_mutex_unlock(&pi_state->pi_mutex);
 
         return 0;
@@ -1236,6 +1250,7 @@ static int do_futex_lock_pi(u32 __user *uaddr, int detect, int trylock,
                 /* 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
@@ -1244,6 +1259,7 @@ static int do_futex_lock_pi(u32 __user *uaddr, int detect, int trylock,
                 q.pi_state->owner = current;
 
                 spin_lock_irq(&current->pi_lock);
+                WARN_ON(!list_empty(&q.pi_state->list));
                 list_add(&q.pi_state->list, &current->pi_state_list);
                 spin_unlock_irq(&current->pi_lock);