From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
huang ying <huang.ying.caritas@gmail.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH-tip v3 11/14] locking/rwsem: Add more rwsem owner access helpers
Date: Wed, 10 Apr 2019 14:42:28 -0400 [thread overview]
Message-ID: <20190410184231.6748-12-longman@redhat.com> (raw)
In-Reply-To: <20190410184231.6748-1-longman@redhat.com>
Before combining owner and count, we are adding two new helpers for
accessing the owner value in the rwsem.
1) struct task_struct *rwsem_get_owner(struct rw_semaphore *sem)
2) bool is_rwsem_reader_owned(struct rw_semaphore *sem)
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/rwsem-xadd.c | 15 ++++++++++-----
kernel/locking/rwsem.c | 3 +--
kernel/locking/rwsem.h | 32 ++++++++++++++++++++++++++------
3 files changed, 37 insertions(+), 13 deletions(-)
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 09b245e0d6f4..196729fd7f94 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -312,7 +312,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
preempt_disable();
rcu_read_lock();
- owner = READ_ONCE(sem->owner);
+ owner = rwsem_get_owner(sem);
if (owner) {
ret = is_rwsem_owner_spinnable(owner) &&
(is_rwsem_owner_reader(owner) || owner_on_cpu(owner));
@@ -344,15 +344,21 @@ enum owner_state {
static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem)
{
- struct task_struct *owner = READ_ONCE(sem->owner);
+ struct task_struct *owner = rwsem_get_owner(sem);
long count;
if (!is_rwsem_owner_spinnable(owner))
return OWNER_NONSPINNABLE;
rcu_read_lock();
- while (owner && !is_rwsem_owner_reader(owner)
- && (READ_ONCE(sem->owner) == owner)) {
+ while (owner && !is_rwsem_owner_reader(owner)) {
+ struct task_struct *new_owner = rwsem_get_owner(sem);
+
+ if (new_owner != owner) {
+ owner = new_owner;
+ break; /* The owner has changed */
+ }
+
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking sem->owner still matches owner, if that fails,
@@ -379,7 +385,6 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem)
* spinning except when here is no active locks and the handoff bit
* is set. In this case, we have to stop spinning.
*/
- owner = READ_ONCE(sem->owner);
if (!is_rwsem_owner_spinnable(owner))
return OWNER_NONSPINNABLE;
if (owner && !is_rwsem_owner_reader(owner))
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index ccbf18f560ff..38d24676e01c 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -198,8 +198,7 @@ EXPORT_SYMBOL(down_write_killable_nested);
void up_read_non_owner(struct rw_semaphore *sem)
{
- DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED),
- sem);
+ DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
__up_read(sem);
}
diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index 19ae51ff7b91..ef7287f273fe 100644
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -92,6 +92,11 @@ static inline void rwsem_clear_owner(struct rw_semaphore *sem)
WRITE_ONCE(sem->owner, NULL);
}
+static inline struct task_struct *rwsem_get_owner(struct rw_semaphore *sem)
+{
+ return READ_ONCE(sem->owner);
+}
+
/*
* The task_struct pointer of the last owning reader will be left in
* the owner field.
@@ -136,6 +141,23 @@ static inline bool is_rwsem_spinnable(struct rw_semaphore *sem)
return is_rwsem_owner_spinnable(READ_ONCE(sem->owner));
}
+/*
+ * Return true if the rwsem is owned by a reader.
+ */
+static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
+{
+#ifdef CONFIG_DEBUG_RWSEMS
+ /*
+ * Check the count to see if it is write-locked.
+ */
+ long count = atomic_long_read(&sem->count);
+
+ if (count & RWSEM_WRITER_MASK)
+ return false;
+#endif
+ return (unsigned long)sem->owner & RWSEM_READER_OWNED;
+}
+
/*
* Return true if rwsem is owned by an anonymous writer or readers.
*/
@@ -155,6 +177,7 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
{
unsigned long val = (unsigned long)current | RWSEM_READER_OWNED
| RWSEM_ANONYMOUSLY_OWNED;
+
if (READ_ONCE(sem->owner) == (struct task_struct *)val)
cmpxchg_relaxed((unsigned long *)&sem->owner, val,
RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED);
@@ -196,8 +219,7 @@ static inline void __down_read(struct rw_semaphore *sem)
if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS,
&sem->count) & RWSEM_READ_FAILED_MASK)) {
rwsem_down_read_failed(sem);
- DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
- RWSEM_READER_OWNED), sem);
+ DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
}
@@ -209,8 +231,7 @@ static inline int __down_read_killable(struct rw_semaphore *sem)
&sem->count) & RWSEM_READ_FAILED_MASK)) {
if (IS_ERR(rwsem_down_read_failed_killable(sem)))
return -EINTR;
- DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
- RWSEM_READER_OWNED), sem);
+ DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
}
@@ -277,8 +298,7 @@ static inline void __up_read(struct rw_semaphore *sem)
{
long tmp;
- DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED),
- sem);
+ DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
rwsem_clear_reader_owned(sem);
tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS))
--
2.18.1
next prev parent reply other threads:[~2019-04-10 18:43 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-10 18:42 [PATCH-tip v3 00/14] locking/rwsem: Rwsem rearchitecture part 2 Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 01/14] locking/rwsem: Prevent unneeded warning during locking selftest Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 02/14] locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER Waiman Long
2019-04-11 8:12 ` Peter Zijlstra
2019-04-11 16:03 ` Waiman Long
2019-04-12 7:02 ` Ingo Molnar
2019-04-12 7:05 ` Peter Zijlstra
2019-04-12 7:09 ` Ingo Molnar
2019-04-12 14:04 ` Waiman Long
2019-04-12 14:07 ` Waiman Long
2019-04-12 14:22 ` Waiman Long
2019-04-12 16:41 ` Ingo Molnar
2019-04-12 18:05 ` Waiman Long
2019-04-13 2:24 ` Waiman Long
2019-04-15 13:43 ` Waiman Long
2019-04-16 7:53 ` Ingo Molnar
2019-04-12 18:21 ` Peter Zijlstra
2019-04-10 18:42 ` [PATCH-tip v3 03/14] locking/rwsem: Implement a new locking scheme Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 04/14] locking/rwsem: Implement lock handoff to prevent lock starvation Waiman Long
2019-04-10 19:38 ` Peter Zijlstra
2019-04-10 20:28 ` Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 05/14] locking/rwsem: Remove rwsem_wake() wakeup optimization Waiman Long
2019-04-11 7:25 ` Peter Zijlstra
2019-04-11 15:55 ` Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 06/14] locking/rwsem: Make rwsem_spin_on_owner() return owner state Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 07/14] locking/rwsem: Ensure an RT task will not spin on reader Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 08/14] locking/rwsem: Wake up almost all readers in wait queue Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 09/14] locking/rwsem: Enable readers spinning on writer Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 10/14] locking/rwsem: Enable time-based spinning on reader-owned rwsem Waiman Long
2019-04-10 18:42 ` Waiman Long [this message]
2019-04-10 18:42 ` [PATCH-tip v3 12/14] locking/rwsem: Guard against making count negative Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 13/14] locking/rwsem: Merge owner into count on x86-64 Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 14/14] locking/rwsem: Remove redundant computation of writer lock word Waiman Long
2019-04-11 8:37 ` [PATCH-tip v3 00/14] locking/rwsem: Rwsem rearchitecture part 2 Peter Zijlstra
2019-04-11 16:09 ` Waiman Long
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