[patch 4/5] futex: Split out the first waiter attachment from lookup_pi_state()

[Thomas Gleixner]

We want to be a bit more clever in futex_lock_pi_atomic() and separate
the possible states. Split out the code which attaches the first
waiter to the owner into a separate function. No functional change.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/futex.c |   42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

Index: linux/kernel/futex.c
===================================================================
--- linux.orig/kernel/futex.c
+++ linux/kernel/futex.c
@@ -865,21 +865,16 @@ out_state:
 	return 0;
 }
 
-static int
-lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
-		union futex_key *key, struct futex_pi_state **ps)
+/*
+ * Lookup the task for the TID provided from user space and attach to
+ * it after doing proper sanity checks.
+ */
+static int attach_to_pi_owner(u32 uval, union futex_key *key,
+			      struct futex_pi_state **ps)
 {
-	struct futex_q *match = futex_top_waiter(hb, key);
-	struct futex_pi_state *pi_state = NULL;
-	struct task_struct *p;
 	pid_t pid = uval & FUTEX_TID_MASK;
-
-	/*
-	 * If there is a waiter on that futex, validate it and
-	 * attach to the pi_state when the validation succeeds.
-	 */
-	if (match)
-		return attach_to_pi_state(uval, match->pi_state, ps);
+	struct futex_pi_state *pi_state;
+	struct task_struct *p;
 
 	/*
 	 * We are the first waiter - try to look up the real owner and attach
@@ -922,7 +917,7 @@ lookup_pi_state(u32 uval, struct futex_h
 	pi_state = alloc_pi_state();
 
 	/*
-	 * Initialize the pi_mutex in locked state and make 'p'
+	 * Initialize the pi_mutex in locked state and make @p
 	 * the owner of it:
 	 */
 	rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
@@ -942,6 +937,25 @@ lookup_pi_state(u32 uval, struct futex_h
 	return 0;
 }
 
+static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
+			   union futex_key *key, struct futex_pi_state **ps)
+{
+	struct futex_q *match = futex_top_waiter(hb, key);
+
+	/*
+	 * If there is a waiter on that futex, validate it and
+	 * attach to the pi_state when the validation succeeds.
+	 */
+	if (match)
+		return attach_to_pi_state(uval, match->pi_state, ps);
+
+	/*
+	 * We are the first waiter - try to look up the owner based on
+	 * @uval and attach to it.
+	 */
+	return attach_to_pi_owner(uval, key, ps);
+}
+
 /**
  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
  * @uaddr:		the pi futex user address


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