Hi Thomas,
I see an application hang in 2.6.31.4-rt14 when running some java tests.
The kernel seems to be continuously looping in
futex_wait_requeue_pi -> futex_wait_setup ->
ret -EAGAIN -> goto retry -> futex_wait_setup -> on and on
===============================================================================
java-5544 [001] 79682.800631: __might_sleep <-rt_spin_lock_fastlock
java-5544 [001] 79682.800631: get_futex_value_locked <-futex_wait_setup
java-5544 [001] 79682.800632: pagefault_disable <-get_futex_value_locked
java-5544 [001] 79682.800632: pagefault_enable <-get_futex_value_locked
java-5544 [001] 79682.800632: queue_unlock <-futex_wait_setup
java-5544 [001] 79682.800632: rt_spin_unlock <-queue_unlock
java-5544 [001] 79682.800633: rt_spin_lock_fastunlock <-rt_spin_unlock
java-5544 [001] 79682.800633: drop_futex_key_refs <-queue_unlock
java-5544 [001] 79682.800633: put_futex_key <-futex_wait_setup
java-5544 [001] 79682.800633: drop_futex_key_refs <-put_futex_key
java-5544 [001] 79682.800633: put_futex_key <-do_futex
java-5544 [001] 79682.800634: drop_futex_key_refs <-put_futex_key
java-5544 [001] 79682.800634: get_futex_key <-do_futex
java-5544 [001] 79682.800634: get_futex_key_refs <-get_futex_key
java-5544 [001] 79682.800634: futex_wait_setup <-do_futex
java-5544 [001] 79682.800635: get_futex_key <-futex_wait_setup
java-5544 [001] 79682.800635: get_futex_key_refs <-get_futex_key
java-5544 [001] 79682.800635: queue_lock <-futex_wait_setup
java-5544 [001] 79682.800635: get_futex_key_refs <-queue_lock
java-5544 [001] 79682.800635: hash_futex <-queue_lock
java-5544 [001] 79682.800636: rt_spin_lock <-queue_lock
java-5544 [001] 79682.800636: rt_spin_lock_fastlock <-rt_spin_lock
java-5544 [001] 79682.800636: __might_sleep <-rt_spin_lock_fastlock
java-5544 [001] 79682.800636: get_futex_value_locked <-futex_wait_setup
java-5544 [001] 79682.800637: pagefault_disable <-get_futex_value_locked
java-5544 [001] 79682.800637: pagefault_enable <-get_futex_value_locked
java-5544 [001] 79682.800637: queue_unlock <-futex_wait_setup
java-5544 [001] 79682.800637: rt_spin_unlock <-queue_unlock
java-5544 [001] 79682.800637: rt_spin_lock_fastunlock <-rt_spin_unlock
java-5544 [001] 79682.800638: drop_futex_key_refs <-queue_unlock
java-5544 [001] 79682.800638: put_futex_key <-futex_wait_setup
java-5544 [001] 79682.800638: drop_futex_key_refs <-put_futex_key
java-5544 [001] 79682.800638: put_futex_key <-do_futex
java-5544 [001] 79682.800639: drop_futex_key_refs <-put_futex_key
java-5544 [001] 79682.800639: get_futex_key <-do_futex
java-5544 [001] 79682.800639: get_futex_key_refs <-get_futex_key
java-5544 [001] 79682.800639: futex_wait_setup <-do_futex
java-5544 [001] 79682.800639: get_futex_key <-futex_wait_setup
java-5544 [001] 79682.800640: get_futex_key_refs <-get_futex_key
java-5544 [001] 79682.800640: queue_lock <-futex_wait_setup
java-5544 [001] 79682.800640: get_futex_key_refs <-queue_lock
java-5544 [001] 79682.800640: hash_futex <-queue_lock
java-5544 [001] 79682.800640: rt_spin_lock <-queue_lock
java-5544 [001] 79682.800641: rt_spin_lock_fastlock <-rt_spin_lock
java-5544 [001] 79682.800641: __might_sleep <-rt_spin_lock_fastlock
java-5544 [001] 79682.800641: get_futex_value_locked <-futex_wait_setup
java-5544 [001] 79682.800641: pagefault_disable <-get_futex_value_locked
java-5544 [001] 79682.800642: pagefault_enable <-get_futex_value_locked
java-5544 [001] 79682.800642: queue_unlock <-futex_wait_setup
java-5544 [001] 79682.800642: rt_spin_unlock <-queue_unlock
java-5544 [001] 79682.800642: rt_spin_lock_fastunlock <-rt_spin_unlock
===============================================================================
This looks to be caused by the patch below
-> http://patchwork.kernel.org/patch/53483/
Not sure if this the best way to go here, but the patch below seems to resolve
the problem for me
If this is fine, I'll send a separate patch for mainline. Currently mainline
seems to be missing the earlier patch referenced above as well
Signed-off-by: Dinakar Guniguntala <dino@xxxxxxxxxx>
-Dinakar
---
kernel/futex.c | 84 +++++++++++++++++++++------------------------------------
1 file changed, 32 insertions(+), 52 deletions(-)
Index: linux-2.6.31.4-rt14-lbf-f1/kernel/futex.c
===================================================================
--- linux-2.6.31.4-rt14-lbf-f1.orig/kernel/futex.c
+++ linux-2.6.31.4-rt14-lbf-f1/kernel/futex.c
@@ -2048,54 +2048,6 @@ pi_faulted:
}
/**
- * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
- * @hb: the hash_bucket futex_q was original enqueued on
- * @q: the futex_q woken while waiting to be requeued
- * @key2: the futex_key of the requeue target futex
- * @timeout: the timeout associated with the wait (NULL if none)
- *
- * Detect if the task was woken on the initial futex as opposed to the requeue
- * target futex. If so, determine if it was a timeout or a signal that caused
- * the wakeup and return the appropriate error code to the caller. Must be
- * called with the hb lock held.
- *
- * Returns
- * 0 - no early wakeup detected
- * <0 - -ETIMEDOUT or -ERESTARTNOINTR
- */
-static inline
-int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
- struct futex_q *q, union futex_key *key2,
- struct hrtimer_sleeper *timeout)
-{
- int ret = 0;
-
- /*
- * With the hb lock held, we avoid races while we process the wakeup.
- * We only need to hold hb (and not hb2) to ensure atomicity as the
- * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
- * It can't be requeued from uaddr2 to something else since we don't
- * support a PI aware source futex for requeue.
- */
- if (!match_futex(&q->key, key2)) {
- WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
- /*
- * We were woken prior to requeue by a timeout or a signal.
- * Unqueue the futex_q and determine which it was.
- */
- plist_del(&q->list, &q->list.plist);
-
- /* Handle spurious wakeups gracefully */
- ret = -EAGAIN;
- if (timeout && !timeout->task)
- ret = -ETIMEDOUT;
- else if (signal_pending(current))
- ret = -ERESTARTNOINTR;
- }
- return ret;
-}
-
-/**
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
* @uaddr: the futex we initialyl wait on (non-pi)
* @fshared: whether the futexes are shared (1) or not (0). They must be
@@ -2186,8 +2138,39 @@ retry:
futex_wait_queue_me(hb, &q, to);
spin_lock(&hb->lock);
- ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
+ /*
+ * Detect if the task was woken on the initial futex as opposed to the requeue
+ * target futex. If so, determine if it was a timeout or a signal that caused
+ * the wakeup and return the appropriate error code to the caller. Must be
+ * called with the hb lock held.
+ * With the hb lock held, we avoid races while we process the wakeup.
+ * We only need to hold hb (and not hb2) to ensure atomicity as the
+ * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
+ * It can't be requeued from uaddr2 to something else since we don't
+ * support a PI aware source futex for requeue.
+ */
+ if (!match_futex(&q.key, &key2)) {
+ WARN_ON(q.lock_ptr && (&hb->lock != q.lock_ptr));
+ /*
+ * We were woken prior to requeue by a timeout or a signal.
+ * Unqueue the futex_q and determine which it was.
+ */
+ plist_del(&q.list, &q.list.plist);
+
+ /* Handle spurious wakeups gracefully */
+ ret = -EAGAIN;
+ if (to && !to->task)
+ ret = -ETIMEDOUT;
+ else if (signal_pending(current))
+ ret = -ERESTARTNOINTR;
+ }
spin_unlock(&hb->lock);
+ if (ret == -EAGAIN) {
+ /* Retry on spurious wakeup */
+ put_futex_key(fshared, &q.key);
+ put_futex_key(fshared, &key2);
+ goto retry;
+ }
if (ret)
goto out_put_keys;
@@ -2264,9 +2247,6 @@ out_put_keys:
out_key2:
put_futex_key(fshared, &key2);
- /* Spurious wakeup ? */
- if (ret == -EAGAIN)
- goto retry;
out:
if (to) {
hrtimer_cancel(&to->timer);
--
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