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Message-Id: <1549566446-27967-15-git-send-email-longman@redhat.com>
Date: Thu, 7 Feb 2019 14:07:18 -0500
From: Waiman Long <longman@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Will Deacon <will.deacon@....com>,
Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org,
sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
linux-arch@...r.kernel.org, x86@...nel.org,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Davidlohr Bueso <dave@...olabs.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Waiman Long <longman@...hat.com>
Subject: [PATCH-tip 14/22] locking/rwsem: Add more rwsem owner access helpers
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@...hat.com>
---
kernel/locking/rwsem-xadd.c | 11 ++++++-----
kernel/locking/rwsem-xadd.h | 32 ++++++++++++++++++++++++++------
kernel/locking/rwsem.c | 3 +--
3 files changed, 33 insertions(+), 13 deletions(-)
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 5f74bae..719d390 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -277,7 +277,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
return false;
rcu_read_lock();
- owner = READ_ONCE(sem->owner);
+ owner = rwsem_get_owner(sem);
if (owner) {
ret = is_rwsem_owner_spinnable(owner) &&
owner_on_cpu(owner);
@@ -291,13 +291,13 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
*/
static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
{
- struct task_struct *owner = READ_ONCE(sem->owner);
+ struct task_struct *owner = rwsem_get_owner(sem);
if (!is_rwsem_owner_spinnable(owner))
return false;
rcu_read_lock();
- while (owner && (READ_ONCE(sem->owner) == owner)) {
+ while (owner && (rwsem_get_owner(sem) == owner)) {
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking sem->owner still matches owner, if that fails,
@@ -323,7 +323,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
* If there is a new owner or the owner is not set, we continue
* spinning.
*/
- return is_rwsem_owner_spinnable(READ_ONCE(sem->owner));
+ return is_rwsem_owner_spinnable(rwsem_get_owner(sem));
}
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
@@ -361,7 +361,8 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
* we're an RT task that will live-lock because we won't let
* the owner complete.
*/
- if (!sem->owner && (need_resched() || rt_task(current)))
+ if (!rwsem_get_owner(sem) &&
+ (need_resched() || rt_task(current)))
break;
/*
diff --git a/kernel/locking/rwsem-xadd.h b/kernel/locking/rwsem-xadd.h
index 6d4890d..277a134 100644
--- a/kernel/locking/rwsem-xadd.h
+++ b/kernel/locking/rwsem-xadd.h
@@ -83,6 +83,11 @@ 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.
@@ -116,6 +121,23 @@ static inline bool is_rwsem_owner_spinnable(struct task_struct *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.
*/
static inline bool rwsem_has_anonymous_owner(struct task_struct *owner)
@@ -135,6 +157,7 @@ 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);
@@ -181,8 +204,7 @@ 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);
}
@@ -194,8 +216,7 @@ 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);
}
@@ -254,8 +275,7 @@ 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))
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index bdfca7c..79fa6e4 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -203,8 +203,7 @@ int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
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);
}
--
1.8.3.1
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