Merge tag 'v4.0-rc1' into locking/core, to refresh the tree before merging new changes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/futex.c b/kernel/futex.c
index 2a5e383..2579e40 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -900,7 +900,7 @@
if (!p)
return -ESRCH;
- if (!p->mm) {
+ if (unlikely(p->flags & PF_KTHREAD)) {
put_task_struct(p);
return -EPERM;
}
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 94674e5..43bf25e 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -25,7 +25,7 @@
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
-#include "mcs_spinlock.h"
+#include <linux/osq_lock.h>
/*
* In the DEBUG case we are using the "NULL fastpath" for mutexes,
@@ -217,44 +217,41 @@
}
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
-{
- if (lock->owner != owner)
- return false;
-
- /*
- * Ensure we emit the owner->on_cpu, dereference _after_ checking
- * lock->owner still matches owner, if that fails, owner might
- * point to free()d memory, if it still matches, the rcu_read_lock()
- * ensures the memory stays valid.
- */
- barrier();
-
- return owner->on_cpu;
-}
-
/*
* Look out! "owner" is an entirely speculative pointer
* access and not reliable.
*/
static noinline
-int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
+bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
{
+ bool ret;
+
rcu_read_lock();
- while (owner_running(lock, owner)) {
- if (need_resched())
+ while (true) {
+ /* Return success when the lock owner changed */
+ if (lock->owner != owner) {
+ ret = true;
break;
+ }
+
+ /*
+ * Ensure we emit the owner->on_cpu, dereference _after_
+ * checking lock->owner still matches owner, if that fails,
+ * owner might point to free()d memory, if it still matches,
+ * the rcu_read_lock() ensures the memory stays valid.
+ */
+ barrier();
+
+ if (!owner->on_cpu || need_resched()) {
+ ret = false;
+ break;
+ }
cpu_relax_lowlatency();
}
rcu_read_unlock();
- /*
- * We break out the loop above on need_resched() and when the
- * owner changed, which is a sign for heavy contention. Return
- * success only when lock->owner is NULL.
- */
- return lock->owner == NULL;
+ return ret;
}
/*
diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index 2555ae1..3a50485 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -85,6 +85,13 @@
list_del(&waiter->list);
tsk = waiter->task;
+ /*
+ * Make sure we do not wakeup the next reader before
+ * setting the nil condition to grant the next reader;
+ * otherwise we could miss the wakeup on the other
+ * side and end up sleeping again. See the pairing
+ * in rwsem_down_read_failed().
+ */
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 2f7cc40..e4ad019 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -14,8 +14,9 @@
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched/rt.h>
+#include <linux/osq_lock.h>
-#include "mcs_spinlock.h"
+#include "rwsem.h"
/*
* Guide to the rw_semaphore's count field for common values.
@@ -186,6 +187,13 @@
waiter = list_entry(next, struct rwsem_waiter, list);
next = waiter->list.next;
tsk = waiter->task;
+ /*
+ * Make sure we do not wakeup the next reader before
+ * setting the nil condition to grant the next reader;
+ * otherwise we could miss the wakeup on the other
+ * side and end up sleeping again. See the pairing
+ * in rwsem_down_read_failed().
+ */
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
@@ -258,6 +266,7 @@
RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) {
if (!list_is_singular(&sem->wait_list))
rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
+ rwsem_set_owner(sem);
return true;
}
@@ -277,8 +286,10 @@
return false;
old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_WRITE_BIAS);
- if (old == count)
+ if (old == count) {
+ rwsem_set_owner(sem);
return true;
+ }
count = old;
}
@@ -287,23 +298,30 @@
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
- bool on_cpu = false;
+ bool ret = true;
if (need_resched())
return false;
rcu_read_lock();
owner = ACCESS_ONCE(sem->owner);
- if (owner)
- on_cpu = owner->on_cpu;
- rcu_read_unlock();
+ if (!owner) {
+ long count = ACCESS_ONCE(sem->count);
+ /*
+ * If sem->owner is not set, yet we have just recently entered the
+ * slowpath with the lock being active, then there is a possibility
+ * reader(s) may have the lock. To be safe, bail spinning in these
+ * situations.
+ */
+ if (count & RWSEM_ACTIVE_MASK)
+ ret = false;
+ goto done;
+ }
- /*
- * If sem->owner is not set, yet we have just recently entered the
- * slowpath, then there is a possibility reader(s) may have the lock.
- * To be safe, avoid spinning in these situations.
- */
- return on_cpu;
+ ret = owner->on_cpu;
+done:
+ rcu_read_unlock();
+ return ret;
}
static inline bool owner_running(struct rw_semaphore *sem,
@@ -326,21 +344,30 @@
static noinline
bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
{
+ long count;
+
rcu_read_lock();
while (owner_running(sem, owner)) {
- if (need_resched())
- break;
+ /* abort spinning when need_resched */
+ if (need_resched()) {
+ rcu_read_unlock();
+ return false;
+ }
cpu_relax_lowlatency();
}
rcu_read_unlock();
+ if (READ_ONCE(sem->owner))
+ return true; /* new owner, continue spinning */
+
/*
- * We break out the loop above on need_resched() or when the
- * owner changed, which is a sign for heavy contention. Return
- * success only when sem->owner is NULL.
+ * When the owner is not set, the lock could be free or
+ * held by readers. Check the counter to verify the
+ * state.
*/
- return sem->owner == NULL;
+ count = READ_ONCE(sem->count);
+ return (count == 0 || count == RWSEM_WAITING_BIAS);
}
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index e2d3bc7..205be0c 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -9,29 +9,9 @@
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rwsem.h>
-
#include <linux/atomic.h>
-#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
-static inline void rwsem_set_owner(struct rw_semaphore *sem)
-{
- sem->owner = current;
-}
-
-static inline void rwsem_clear_owner(struct rw_semaphore *sem)
-{
- sem->owner = NULL;
-}
-
-#else
-static inline void rwsem_set_owner(struct rw_semaphore *sem)
-{
-}
-
-static inline void rwsem_clear_owner(struct rw_semaphore *sem)
-{
-}
-#endif
+#include "rwsem.h"
/*
* lock for reading
diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
new file mode 100644
index 0000000..870ed9a
--- /dev/null
+++ b/kernel/locking/rwsem.h
@@ -0,0 +1,20 @@
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+static inline void rwsem_set_owner(struct rw_semaphore *sem)
+{
+ sem->owner = current;
+}
+
+static inline void rwsem_clear_owner(struct rw_semaphore *sem)
+{
+ sem->owner = NULL;
+}
+
+#else
+static inline void rwsem_set_owner(struct rw_semaphore *sem)
+{
+}
+
+static inline void rwsem_clear_owner(struct rw_semaphore *sem)
+{
+}
+#endif
