[TIP][RFC 2/7] futex: futex_top_waiter()

[Darren Hart <dvhltc@us.ibm.com>]

From: Darren Hart <dvhltc@us.ibm.com>

Improve legibility by wrapping finding the top waiter in a function.  This
will be used by the follow-on patches for enabling requeue pi.

Changelog:
V4: -Simplified logic in the hb loop
    -Return the futex_q as the task can be had from there if needed
    -Updated comments and dropped the -safe iterator per review from tglx
V3: -Comment linewidth cleanup
V1: -Initial version

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
---

 kernel/futex.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)


diff --git a/kernel/futex.c b/kernel/futex.c
index 16459c2..d02962b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -277,6 +277,32 @@ void put_futex_key(int fshared, union futex_key *key)
 	drop_futex_key_refs(key);
 }
 
+/*
+ * futex_top_waiter - return the highest priority waiter on the futex specified
+ *                    by key
+ * @hb: the hash bucket the futex_q's reside in
+ * @key: the futex key (to distinguish it from other futex futex_q's)
+ *
+ * Must be called with the hb lock held.
+ *
+ */
+static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
+					union futex_key *key)
+{
+	struct plist_head *head;
+	struct futex_q *this;
+	struct futex_q *top_waiter = NULL;
+
+	head = &hb->chain;
+	plist_for_each_entry(this, head, list) {
+		if (match_futex(&this->key, key)) {
+			top_waiter = this;
+			break;
+		}
+	}
+	return top_waiter;
+}
+
 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
 {
 	u32 curval;
-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team