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Subject[tip PATCH v7 8/9] RFC: futex: add futex_wait_setup()
Date
Refactor the code to validate the expected futex value in order to
reuse it with the requeue_pi code.

Changelog:
V7: -Initial version

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sripathi Kodi <sripathik@in.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Dinakar Guniguntala <dino@in.ibm.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jakub Jelinek <jakub@redhat.com>
---
kernel/futex.c | 116 +++++++++++++++++++++++++++++++++++---------------------
1 files changed, 72 insertions(+), 44 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 4fa5de1..bf657db 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1398,42 +1398,29 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
__set_current_state(TASK_RUNNING);
}

-static int futex_wait(u32 __user *uaddr, int fshared,
- u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
+/**
+ * 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)
{
- struct hrtimer_sleeper timeout, *to = NULL;
- DECLARE_WAITQUEUE(wait, current);
- struct restart_block *restart;
- struct futex_hash_bucket *hb;
- struct futex_q q;
u32 uval;
int ret;

- if (!bitset)
- return -EINVAL;
-
- q.pi_state = NULL;
- q.bitset = bitset;
-
- if (abs_time) {
- to = &timeout;
-
- hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
- CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
- hrtimer_init_sleeper(to, current);
- hrtimer_set_expires_range_ns(&to->timer, *abs_time,
- current->timer_slack_ns);
- }
-
-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);
-
/*
* Access the page AFTER the hash-bucket is locked.
* Order is important:
@@ -1450,33 +1437,74 @@ retry_private:
* 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.
*/
+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 (unlikely(ret)) {
- queue_unlock(&q, hb);
+ if (ret) {
+ queue_unlock(q, *hb);

ret = get_user(uval, uaddr);
if (ret)
- goto out_put_key;
+ goto out;

if (!fshared)
goto retry_private;

- put_futex_key(fshared, &q.key);
+ 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;
+ 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)
+{
+ struct hrtimer_sleeper timeout, *to = NULL;
+ DECLARE_WAITQUEUE(wait, current);
+ struct restart_block *restart;
+ struct futex_hash_bucket *hb;
+ struct futex_q q;
+ int ret;
+
+ if (!bitset)
+ return -EINVAL;
+
+ q.pi_state = NULL;
+ q.bitset = bitset;
+
+ if (abs_time) {
+ to = &timeout;
+
+ hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
+ CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init_sleeper(to, current);
+ hrtimer_set_expires_range_ns(&to->timer, *abs_time,
+ current->timer_slack_ns);
+ }
+
+ /* Prepare to wait on uaddr. */
+ ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
+ if (ret)
+ goto out;
+
/* queue_me and wait for wakeup, timeout, or a signal. */
futex_wait_queue_me(hb, &q, to, &wait);



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