| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Fri, 5 Apr 2019 15:21:12 -0400
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, x86@...nel.org,
Davidlohr Bueso <dave@...olabs.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Waiman Long <longman@...hat.com>
Subject: [PATCH-tip v2 09/12] 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 | 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 bc3fd14cf354..a9756e3e3a73 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 1398799b7547..bbb8a266dd50 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.
*/
@@ -156,6 +178,7 @@ 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);
@@ -218,8 +241,7 @@ 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);
}
@@ -231,8 +253,7 @@ 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);
}
@@ -299,8 +320,7 @@ 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
Powered by blists - more mailing lists