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authorTim Chen <tim.c.chen@linux.intel.com>2014-01-21 15:36:00 -0800
committerIngo Molnar <mingo@kernel.org>2014-01-28 13:13:27 +0100
commite72246748ff006ab928bc774e276e6ef5542f9c5 (patch)
treeb3021f1615d2088ce20fc02bd61e9f2baab72dd1 /kernel/locking
parentaff7385b5a16bca6b8d9243f01a9ea5a5b411e1d (diff)
locking/mutexes/mcs: Restructure the MCS lock defines and locking code into its own file
We will need the MCS lock code for doing optimistic spinning for rwsem and queued rwlock. Extracting the MCS code from mutex.c and put into its own file allow us to reuse this code easily. We also inline mcs_spin_lock and mcs_spin_unlock functions for better efficiency. Note that using the smp_load_acquire/smp_store_release pair used in mcs_lock and mcs_unlock is not sufficient to form a full memory barrier across cpus for many architectures (except x86). For applications that absolutely need a full barrier across multiple cpus with mcs_unlock and mcs_lock pair, smp_mb__after_unlock_lock() should be used after mcs_lock. Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1390347360.3138.63.camel@schen9-DESK Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/mutex.c68
1 files changed, 7 insertions, 61 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index fbbd2eda867e..45fe1b5293d6 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -25,6 +25,7 @@
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
+#include <linux/mcs_spinlock.h>
/*
* In the DEBUG case we are using the "NULL fastpath" for mutexes,
@@ -52,7 +53,7 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
INIT_LIST_HEAD(&lock->wait_list);
mutex_clear_owner(lock);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
- lock->spin_mlock = NULL;
+ lock->mcs_lock = NULL;
#endif
debug_mutex_init(lock, name, key);
@@ -111,62 +112,7 @@ EXPORT_SYMBOL(mutex_lock);
* more or less simultaneously, the spinners need to acquire a MCS lock
* first before spinning on the owner field.
*
- * We don't inline mspin_lock() so that perf can correctly account for the
- * time spent in this lock function.
*/
-struct mspin_node {
- struct mspin_node *next ;
- int locked; /* 1 if lock acquired */
-};
-#define MLOCK(mutex) ((struct mspin_node **)&((mutex)->spin_mlock))
-
-static noinline
-void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
-{
- struct mspin_node *prev;
-
- /* Init node */
- node->locked = 0;
- node->next = NULL;
-
- prev = xchg(lock, node);
- if (likely(prev == NULL)) {
- /* Lock acquired */
- node->locked = 1;
- return;
- }
- ACCESS_ONCE(prev->next) = node;
- /*
- * Wait until the lock holder passes the lock down.
- * Using smp_load_acquire() provides a memory barrier that
- * ensures subsequent operations happen after the lock is acquired.
- */
- while (!(smp_load_acquire(&node->locked)))
- arch_mutex_cpu_relax();
-}
-
-static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
-{
- struct mspin_node *next = ACCESS_ONCE(node->next);
-
- if (likely(!next)) {
- /*
- * Release the lock by setting it to NULL
- */
- if (cmpxchg(lock, node, NULL) == node)
- return;
- /* Wait until the next pointer is set */
- while (!(next = ACCESS_ONCE(node->next)))
- arch_mutex_cpu_relax();
- }
- /*
- * Pass lock to next waiter.
- * smp_store_release() provides a memory barrier to ensure
- * all operations in the critical section has been completed
- * before unlocking.
- */
- smp_store_release(&next->locked, 1);
-}
/*
* Mutex spinning code migrated from kernel/sched/core.c
@@ -456,7 +402,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
for (;;) {
struct task_struct *owner;
- struct mspin_node node;
+ struct mcs_spinlock node;
if (use_ww_ctx && ww_ctx->acquired > 0) {
struct ww_mutex *ww;
@@ -478,10 +424,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* If there's an owner, wait for it to either
* release the lock or go to sleep.
*/
- mspin_lock(MLOCK(lock), &node);
+ mcs_spin_lock(&lock->mcs_lock, &node);
owner = ACCESS_ONCE(lock->owner);
if (owner && !mutex_spin_on_owner(lock, owner)) {
- mspin_unlock(MLOCK(lock), &node);
+ mcs_spin_unlock(&lock->mcs_lock, &node);
goto slowpath;
}
@@ -496,11 +442,11 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
}
mutex_set_owner(lock);
- mspin_unlock(MLOCK(lock), &node);
+ mcs_spin_unlock(&lock->mcs_lock, &node);
preempt_enable();
return 0;
}
- mspin_unlock(MLOCK(lock), &node);
+ mcs_spin_unlock(&lock->mcs_lock, &node);
/*
* When there's no owner, we might have preempted between the