futex: split out atomic logic from futex_lock_pi()
Refactor the atomic portion of futex_lock_pi() into futex_lock_pi_atomic().
This logic will be needed by requeue_pi, so modularize it to reduce
code duplication. The only significant change is passing of the task
to try and take the lock for. This simplifies the -EDEADLK test as if
the lock is owned by task t, it's a deadlock, regardless of if we are
doing requeue pi or not. This patch updates the corresponding comment
accordingly.
Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/futex.c b/kernel/futex.c
index 421fb5e..986b16e 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -556,6 +556,127 @@
return 0;
}
+/**
+ * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
+ * @uaddr: the pi futex user address
+ * @hb: the pi futex hash bucket
+ * @key: the futex key associated with uaddr and hb
+ * @ps: the pi_state pointer where we store the result of the lookup
+ * @task: the task to perform the atomic lock work for. This will be
+ * "current" except in the case of requeue pi.
+ *
+ * Returns:
+ * 0 - ready to wait
+ * 1 - acquired the lock
+ * <0 - error
+ *
+ * The hb->lock and futex_key refs shall be held by the caller.
+ */
+static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
+ union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct *task)
+{
+ int lock_taken, ret, ownerdied = 0;
+ u32 uval, newval, curval;
+
+retry:
+ ret = lock_taken = 0;
+
+ /*
+ * To avoid races, we attempt to take the lock here again
+ * (by doing a 0 -> TID atomic cmpxchg), while holding all
+ * the locks. It will most likely not succeed.
+ */
+ newval = task_pid_vnr(task);
+
+ curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
+
+ if (unlikely(curval == -EFAULT))
+ return -EFAULT;
+
+ /*
+ * Detect deadlocks.
+ */
+ if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
+ return -EDEADLK;
+
+ /*
+ * Surprise - we got the lock. Just return to userspace:
+ */
+ if (unlikely(!curval))
+ return 1;
+
+ uval = curval;
+
+ /*
+ * Set the FUTEX_WAITERS flag, so the owner will know it has someone
+ * to wake at the next unlock.
+ */
+ newval = curval | FUTEX_WAITERS;
+
+ /*
+ * There are two cases, where a futex might have no owner (the
+ * owner TID is 0): OWNER_DIED. We take over the futex in this
+ * case. We also do an unconditional take over, when the owner
+ * of the futex died.
+ *
+ * This is safe as we are protected by the hash bucket lock !
+ */
+ if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
+ /* Keep the OWNER_DIED bit */
+ newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
+ ownerdied = 0;
+ lock_taken = 1;
+ }
+
+ curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
+
+ if (unlikely(curval == -EFAULT))
+ return -EFAULT;
+ if (unlikely(curval != uval))
+ goto retry;
+
+ /*
+ * We took the lock due to owner died take over.
+ */
+ if (unlikely(lock_taken))
+ return 1;
+
+ /*
+ * We dont have the lock. Look up the PI state (or create it if
+ * we are the first waiter):
+ */
+ ret = lookup_pi_state(uval, hb, key, ps);
+
+ if (unlikely(ret)) {
+ switch (ret) {
+ case -ESRCH:
+ /*
+ * No owner found for this futex. Check if the
+ * OWNER_DIED bit is set to figure out whether
+ * this is a robust futex or not.
+ */
+ if (get_futex_value_locked(&curval, uaddr))
+ return -EFAULT;
+
+ /*
+ * We simply start over in case of a robust
+ * futex. The code above will take the futex
+ * and return happy.
+ */
+ if (curval & FUTEX_OWNER_DIED) {
+ ownerdied = 1;
+ goto retry;
+ }
+ default:
+ break;
+ }
+ }
+
+ return ret;
+}
+
/*
* The hash bucket lock must be held when this is called.
* Afterwards, the futex_q must not be accessed.
@@ -1340,9 +1461,9 @@
struct hrtimer_sleeper timeout, *to = NULL;
struct task_struct *curr = current;
struct futex_hash_bucket *hb;
- u32 uval, newval, curval;
+ u32 uval;
struct futex_q q;
- int ret, lock_taken, ownerdied = 0;
+ int ret;
if (refill_pi_state_cache())
return -ENOMEM;
@@ -1365,81 +1486,15 @@
retry_private:
hb = queue_lock(&q);
-retry_locked:
- ret = lock_taken = 0;
-
- /*
- * To avoid races, we attempt to take the lock here again
- * (by doing a 0 -> TID atomic cmpxchg), while holding all
- * the locks. It will most likely not succeed.
- */
- newval = task_pid_vnr(current);
-
- curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
-
- if (unlikely(curval == -EFAULT))
- goto uaddr_faulted;
-
- /*
- * Detect deadlocks. In case of REQUEUE_PI this is a valid
- * situation and we return success to user space.
- */
- if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(current))) {
- ret = -EDEADLK;
- goto out_unlock_put_key;
- }
-
- /*
- * Surprise - we got the lock. Just return to userspace:
- */
- if (unlikely(!curval))
- goto out_unlock_put_key;
-
- uval = curval;
-
- /*
- * Set the WAITERS flag, so the owner will know it has someone
- * to wake at next unlock
- */
- newval = curval | FUTEX_WAITERS;
-
- /*
- * There are two cases, where a futex might have no owner (the
- * owner TID is 0): OWNER_DIED. We take over the futex in this
- * case. We also do an unconditional take over, when the owner
- * of the futex died.
- *
- * This is safe as we are protected by the hash bucket lock !
- */
- if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
- /* Keep the OWNER_DIED bit */
- newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);
- ownerdied = 0;
- lock_taken = 1;
- }
-
- curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
-
- if (unlikely(curval == -EFAULT))
- goto uaddr_faulted;
- if (unlikely(curval != uval))
- goto retry_locked;
-
- /*
- * We took the lock due to owner died take over.
- */
- if (unlikely(lock_taken))
- goto out_unlock_put_key;
-
- /*
- * We dont have the lock. Look up the PI state (or create it if
- * we are the first waiter):
- */
- ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
-
+ ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current);
if (unlikely(ret)) {
switch (ret) {
-
+ case 1:
+ /* We got the lock. */
+ ret = 0;
+ goto out_unlock_put_key;
+ case -EFAULT:
+ goto uaddr_faulted;
case -EAGAIN:
/*
* Task is exiting and we just wait for the
@@ -1449,25 +1504,6 @@
put_futex_key(fshared, &q.key);
cond_resched();
goto retry;
-
- case -ESRCH:
- /*
- * No owner found for this futex. Check if the
- * OWNER_DIED bit is set to figure out whether
- * this is a robust futex or not.
- */
- if (get_futex_value_locked(&curval, uaddr))
- goto uaddr_faulted;
-
- /*
- * We simply start over in case of a robust
- * futex. The code above will take the futex
- * and return happy.
- */
- if (curval & FUTEX_OWNER_DIED) {
- ownerdied = 1;
- goto retry_locked;
- }
default:
goto out_unlock_put_key;
}
