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

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