spinlock: lockbreak cleanup

The break_lock data structure and code for spinlocks is quite nasty.
Not only does it double the size of a spinlock but it changes locking to
a potentially less optimal trylock.

Put all of that under CONFIG_GENERIC_LOCKBREAK, and introduce a
__raw_spin_is_contended that uses the lock data itself to determine whether
there are waiters on the lock, to be used if CONFIG_GENERIC_LOCKBREAK is
not set.

Rename need_lockbreak to spin_needbreak, make it use spin_is_contended to
decouple it from the spinlock implementation, and make it typesafe (rwlocks
do not have any need_lockbreak sites -- why do they even get bloated up
with that break_lock then?).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 7 insertions, 12 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 524285e46fa7..ba4c88088f62 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4945,19 +4945,15 @@ EXPORT_SYMBOL(_cond_resched);
  */
 int cond_resched_lock(spinlock_t *lock)
 {
+        int resched = need_resched() && system_state == SYSTEM_RUNNING;
         int ret = 0;
 
-        if (need_lockbreak(lock)) {
+        if (spin_needbreak(lock) || resched) {
                 spin_unlock(lock);
-                cpu_relax();
-                ret = 1;
-                spin_lock(lock);
-        }
-        if (need_resched() && system_state == SYSTEM_RUNNING) {
-                spin_release(&lock->dep_map, 1, _THIS_IP_);
-                _raw_spin_unlock(lock);
-                preempt_enable_no_resched();
-                __cond_resched();
+                if (resched && need_resched())
+                        __cond_resched();
+                else
+                        cpu_relax();
                 ret = 1;
                 spin_lock(lock);
         }
diff --git a/kernel/spinlock.c b/kernel/spinlock.c
index cd72424c2662..ae28c8245123 100644
--- a/kernel/spinlock.c
+++ b/kernel/spinlock.c
@@ -65,8 +65,7 @@ EXPORT_SYMBOL(_write_trylock);
  * even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
  * not re-enabled during lock-acquire (which the preempt-spin-ops do):
  */
-#if !defined(CONFIG_PREEMPT) || !defined(CONFIG_SMP) || \
-        defined(CONFIG_DEBUG_LOCK_ALLOC)
+#if !defined(CONFIG_GENERIC_LOCKBREAK) || defined(CONFIG_DEBUG_LOCK_ALLOC)
 
 void __lockfunc _read_lock(rwlock_t *lock)
 {