Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

Pull locking fixes from Ingo Molnar:
 "Misc fixes:

  pvqspinlocks:
   - an instrumentation fix

  futexes:
   - preempt-count vs pagefault_disable decouple corner case fix
   - futex requeue plist race window fix
   - futex UNLOCK_PI transaction fix for a corner case"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  asm-generic/futex: Re-enable preemption in futex_atomic_cmpxchg_inatomic()
  futex: Acknowledge a new waiter in counter before plist
  futex: Handle unlock_pi race gracefully
  locking/pvqspinlock: Fix division by zero in qstat_read()

diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index e56272c..bf2d34c 100644 (file)
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -108,11 +108,15 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
        u32 val;
 
        preempt_disable();
-       if (unlikely(get_user(val, uaddr) != 0))
+       if (unlikely(get_user(val, uaddr) != 0)) {
+               preempt_enable();
                return -EFAULT;
+       }
 
-       if (val == oldval && unlikely(put_user(newval, uaddr) != 0))
+       if (val == oldval && unlikely(put_user(newval, uaddr) != 0)) {
+               preempt_enable();
                return -EFAULT;
+       }
 
        *uval = val;
        preempt_enable();

diff --git a/kernel/futex.c b/kernel/futex.c
index a5d2e74..c20f06f 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1295,10 +1295,20 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
        if (unlikely(should_fail_futex(true)))
                ret = -EFAULT;
 
-       if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
+       if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
                ret = -EFAULT;
-       else if (curval != uval)
-               ret = -EINVAL;
+       } else if (curval != uval) {
+               /*
+                * If a unconditional UNLOCK_PI operation (user space did not
+                * try the TID->0 transition) raced with a waiter setting the
+                * FUTEX_WAITERS flag between get_user() and locking the hash
+                * bucket lock, retry the operation.
+                */
+               if ((FUTEX_TID_MASK & curval) == uval)
+                       ret = -EAGAIN;
+               else
+                       ret = -EINVAL;
+       }
        if (ret) {
                raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
                return ret;
@@ -1525,8 +1535,8 @@ void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
        if (likely(&hb1->chain != &hb2->chain)) {
                plist_del(&q->list, &hb1->chain);
                hb_waiters_dec(hb1);
-               plist_add(&q->list, &hb2->chain);
                hb_waiters_inc(hb2);
+               plist_add(&q->list, &hb2->chain);
                q->lock_ptr = &hb2->lock;
        }
        get_futex_key_refs(key2);
@@ -2622,6 +2632,15 @@ retry:
                 */
                if (ret == -EFAULT)
                        goto pi_faulted;
+               /*
+                * A unconditional UNLOCK_PI op raced against a waiter
+                * setting the FUTEX_WAITERS bit. Try again.
+                */
+               if (ret == -EAGAIN) {
+                       spin_unlock(&hb->lock);
+                       put_futex_key(&key);
+                       goto retry;
+               }
                /*
                 * wake_futex_pi has detected invalid state. Tell user
                 * space.

diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
index eb2a2c9..d734b75 100644 (file)
--- a/kernel/locking/qspinlock_stat.h
+++ b/kernel/locking/qspinlock_stat.h
@@ -136,10 +136,12 @@ static ssize_t qstat_read(struct file *file, char __user *user_buf,
        }
 
        if (counter == qstat_pv_hash_hops) {
-               u64 frac;
+               u64 frac = 0;
 
-               frac = 100ULL * do_div(stat, kicks);
-               frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
+               if (kicks) {
+                       frac = 100ULL * do_div(stat, kicks);
+                       frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
+               }
 
                /*
                 * Return a X.XX decimal number