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>

diff --git a/kernel/futex.c b/kernel/futex.c
index db0c6863e8a35b1d781bb67b2c0adf2b3b4fdfd0..e65b68677d0b678e8a710deaa4054c2c9d8aceff 100644 (file)
--- 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