futex: split out futex value validation code
Refactor the code to validate the expected futex value in order to
reuse it with the requeue_pi code.
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 e76942e..dbe857a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1398,6 +1398,82 @@
__set_current_state(TASK_RUNNING);
}
+/**
+ * futex_wait_setup() - Prepare to wait on a futex
+ * @uaddr: the futex userspace address
+ * @val: the expected value
+ * @fshared: whether the futex is shared (1) or not (0)
+ * @q: the associated futex_q
+ * @hb: storage for hash_bucket pointer to be returned to caller
+ *
+ * Setup the futex_q and locate the hash_bucket. Get the futex value and
+ * compare it with the expected value. Handle atomic faults internally.
+ * Return with the hb lock held and a q.key reference on success, and unlocked
+ * with no q.key reference on failure.
+ *
+ * Returns:
+ * 0 - uaddr contains val and hb has been locked
+ * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
+ */
+static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
+ struct futex_q *q, struct futex_hash_bucket **hb)
+{
+ u32 uval;
+ int ret;
+
+ /*
+ * Access the page AFTER the hash-bucket is locked.
+ * Order is important:
+ *
+ * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
+ * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
+ *
+ * The basic logical guarantee of a futex is that it blocks ONLY
+ * if cond(var) is known to be true at the time of blocking, for
+ * any cond. If we queued after testing *uaddr, that would open
+ * a race condition where we could block indefinitely with
+ * cond(var) false, which would violate the guarantee.
+ *
+ * A consequence is that futex_wait() can return zero and absorb
+ * a wakeup when *uaddr != val on entry to the syscall. This is
+ * rare, but normal.
+ */
+retry:
+ q->key = FUTEX_KEY_INIT;
+ ret = get_futex_key(uaddr, fshared, &q->key);
+ if (unlikely(ret != 0))
+ goto out;
+
+retry_private:
+ *hb = queue_lock(q);
+
+ ret = get_futex_value_locked(&uval, uaddr);
+
+ if (ret) {
+ queue_unlock(q, *hb);
+
+ ret = get_user(uval, uaddr);
+ if (ret)
+ goto out;
+
+ if (!fshared)
+ goto retry_private;
+
+ put_futex_key(fshared, &q->key);
+ goto retry;
+ }
+
+ if (uval != val) {
+ queue_unlock(q, *hb);
+ ret = -EWOULDBLOCK;
+ }
+
+out:
+ if (ret)
+ put_futex_key(fshared, &q->key);
+ return ret;
+}
+
static int futex_wait(u32 __user *uaddr, int fshared,
u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
{
@@ -1406,7 +1482,6 @@
struct restart_block *restart;
struct futex_hash_bucket *hb;
struct futex_q q;
- u32 uval;
int ret;
if (!bitset)
@@ -1425,58 +1500,11 @@
current->timer_slack_ns);
}
-retry:
- q.key = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr, fshared, &q.key);
- if (unlikely(ret != 0))
+ /* Prepare to wait on uaddr. */
+ ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
+ if (ret)
goto out;
-retry_private:
- hb = queue_lock(&q);
-
- /*
- * Access the page AFTER the hash-bucket is locked.
- * Order is important:
- *
- * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
- * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
- *
- * The basic logical guarantee of a futex is that it blocks ONLY
- * if cond(var) is known to be true at the time of blocking, for
- * any cond. If we queued after testing *uaddr, that would open
- * a race condition where we could block indefinitely with
- * cond(var) false, which would violate the guarantee.
- *
- * A consequence is that futex_wait() can return zero and absorb
- * 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
- * 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);
-
- ret = get_user(uval, uaddr);
- if (ret)
- goto out_put_key;
-
- if (!fshared)
- goto retry_private;
-
- put_futex_key(fshared, &q.key);
- goto retry;
- }
- ret = -EWOULDBLOCK;
-
- /* Only actually queue if *uaddr contained val. */
- if (unlikely(uval != val)) {
- queue_unlock(&q, hb);
- goto out_put_key;
- }
-
/* queue_me and wait for wakeup, timeout, or a signal. */
futex_wait_queue_me(hb, &q, to, &wait);