linux-kernel - [tip PATCH v6 2/8] RFC: futex: futex_top

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Date:	Mon, 30 Mar 2009 14:37:47 -0700
From:	Darren Hart <dvhltc@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Sripathi Kodi <sripathik@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <johnstul@...ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>,
	Darren Hart <dvhltc@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sripathi Kodi <sripathik@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <johnstul@...ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>
Subject: [tip PATCH v6 2/8] RFC: futex: futex_top_waiter()

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:
V6: -Shortened function length after review from tglx
    -Corrected kernel-doc formatting
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@...ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Sripathi Kodi <sripathik@...ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: John Stultz <johnstul@...ibm.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Dinakar Guniguntala <dino@...ibm.com>
Cc: Ulrich Drepper <drepper@...hat.com>
Cc: Eric Dumazet <dada1@...mosbay.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Jakub Jelinek <jakub@...hat.com>
---

 kernel/futex.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index b2ed762..8ebed88 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -276,6 +276,25 @@ void put_futex_key(int fshared, union futex_key *key)
 	drop_futex_key_refs(key);
 }
 
+/**
+ * futex_top_waiter() - return the highest priority waiter on a futex
+ * @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 futex_q *this;
+
+	plist_for_each_entry(this, &hb->chain, list) {
+		if (match_futex(&this->key, key))
+			return this;
+	}
+	return NULL;
+}
+
 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
 {
 	u32 curval;

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