futex: Split out the first waiter attachment from lookup_pi_state()

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@linutronix.de>
Reviewed-by: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Kees Cook <kees@outflux.net>
Cc: wad@chromium.org
Link: http://lkml.kernel.org/r/20140611204237.271300614@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 28 insertions, 14 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index db0c6863e8a3..e65b68677d0b 100644
--- a/kernel/futex.c
+++ b/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_hash_bucket *hb,
         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_hash_bucket *hb,
         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