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Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c30
1 files changed, 21 insertions, 9 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 4cdc603b00c3..628be42296eb 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2654,20 +2654,33 @@ retry_private:
goto no_block;
}
+ rt_mutex_init_waiter(&rt_waiter);
+
/*
- * We must add ourselves to the rt_mutex waitlist while holding hb->lock
- * such that the hb and rt_mutex wait lists match.
+ * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
+ * hold it while doing rt_mutex_start_proxy(), because then it will
+ * include hb->lock in the blocking chain, even through we'll not in
+ * fact hold it while blocking. This will lead it to report -EDEADLK
+ * and BUG when futex_unlock_pi() interleaves with this.
+ *
+ * Therefore acquire wait_lock while holding hb->lock, but drop the
+ * latter before calling rt_mutex_start_proxy_lock(). This still fully
+ * serializes against futex_unlock_pi() as that does the exact same
+ * lock handoff sequence.
*/
- rt_mutex_init_waiter(&rt_waiter);
- ret = rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+ raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
+ spin_unlock(q.lock_ptr);
+ ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+ raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
+
if (ret) {
if (ret == 1)
ret = 0;
+ spin_lock(q.lock_ptr);
goto no_block;
}
- spin_unlock(q.lock_ptr);
if (unlikely(to))
hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
@@ -2680,6 +2693,9 @@ retry_private:
* first acquire the hb->lock before removing the lock from the
* rt_mutex waitqueue, such that we can keep the hb and rt_mutex
* wait lists consistent.
+ *
+ * In particular; it is important that futex_unlock_pi() can not
+ * observe this inconsistency.
*/
if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
ret = 0;
@@ -2791,10 +2807,6 @@ retry:
get_pi_state(pi_state);
/*
- * Since modifying the wait_list is done while holding both
- * hb->lock and wait_lock, holding either is sufficient to
- * observe it.
- *
* By taking wait_lock while still holding hb->lock, we ensure
* there is no point where we hold neither; and therefore
* wake_futex_pi() must observe a state consistent with what we