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Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse Source 
Pull core locking changes from Ingo Molnar:
 "Main changes:

   - jump label asm preparatory work for PowerPC (Anton Blanchard)

   - rwsem optimizations and cleanups (Davidlohr Bueso)

   - mutex optimizations and cleanups (Jason Low)

   - futex fix (Oleg Nesterov)

   - remove broken atomicity checks from {READ,WRITE}_ONCE() (Peter
     Zijlstra)"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  powerpc, jump_label: Include linux/jump_label.h to get HAVE_JUMP_LABEL define
  jump_label: Allow jump labels to be used in assembly
  jump_label: Allow asm/jump_label.h to be included in assembly
  locking/mutex: Further simplify mutex_spin_on_owner()
  locking: Remove atomicy checks from {READ,WRITE}_ONCE
  locking/rtmutex: Rename argument in the rt_mutex_adjust_prio_chain() documentation as well
  locking/rwsem: Fix lock optimistic spinning when owner is not running
  locking: Remove ACCESS_ONCE() usage
  locking/rwsem: Check for active lock before bailing on spinning
  locking/rwsem: Avoid deceiving lock spinners
  locking/rwsem: Set lock ownership ASAP
  locking/rwsem: Document barrier need when waking tasks
  locking/futex: Check PF_KTHREAD rather than !p->mm to filter out kthreads
  locking/mutex: Refactor mutex_spin_on_owner()
  locking/mutex: In mutex_spin_on_owner(), return true when owner changes
This commit is contained in:
Linus Torvalds 2015-04-13 10:27:28 -07:00
commit cc76ee75a9
23 changed files with 160 additions and 147 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
Makefile
View File

@ -779,6 +779,7 @@ KBUILD_ARFLAGS := $(call ar-option,D)
# check for 'asm goto'
ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC)), y)
KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
endif
include $(srctree)/scripts/Makefile.kasan

5
arch/arm/include/asm/jump_label.h
View File

@ -1,7 +1,7 @@
#ifndef _ASM_ARM_JUMP_LABEL_H
#define _ASM_ARM_JUMP_LABEL_H
#ifdef __KERNEL__
#ifndef __ASSEMBLY__
#include <linux/types.h>
@ -27,8 +27,6 @@ l_yes:
return true;
}
#endif /* __KERNEL__ */
typedef u32 jump_label_t;
struct jump_entry {
@ -37,4 +35,5 @@ struct jump_entry {
jump_label_t key;
};
#endif /* __ASSEMBLY__ */
#endif

8
arch/arm64/include/asm/jump_label.h
View File

@ -18,11 +18,12 @@
*/
#ifndef __ASM_JUMP_LABEL_H
#define __ASM_JUMP_LABEL_H
#ifndef __ASSEMBLY__
#include <linux/types.h>
#include <asm/insn.h>
#ifdef __KERNEL__
#define JUMP_LABEL_NOP_SIZE AARCH64_INSN_SIZE
static __always_inline bool arch_static_branch(struct static_key *key)
@ -39,8 +40,6 @@ l_yes:
return true;
}
#endif /* __KERNEL__ */
typedef u64 jump_label_t;
struct jump_entry {
@ -49,4 +48,5 @@ struct jump_entry {
jump_label_t key;
};
#endif /* __ASSEMBLY__ */
#endif /* __ASM_JUMP_LABEL_H */

7
arch/mips/include/asm/jump_label.h
View File

@ -8,9 +8,9 @@
#ifndef _ASM_MIPS_JUMP_LABEL_H
#define _ASM_MIPS_JUMP_LABEL_H
#include <linux/types.h>
#ifndef __ASSEMBLY__
#ifdef __KERNEL__
#include <linux/types.h>
#define JUMP_LABEL_NOP_SIZE 4
@ -39,8 +39,6 @@ l_yes:
return true;
}
#endif /* __KERNEL__ */
#ifdef CONFIG_64BIT
typedef u64 jump_label_t;
#else
@ -53,4 +51,5 @@ struct jump_entry {
jump_label_t key;
};
#endif /* __ASSEMBLY__ */
#endif /* _ASM_MIPS_JUMP_LABEL_H */

2
arch/powerpc/platforms/powernv/opal-wrappers.S
View File

@ -9,11 +9,11 @@
* 2 of the License, or (at your option) any later version.
*/
#include <linux/jump_label.h>
#include <asm/ppc_asm.h>
#include <asm/hvcall.h>
#include <asm/asm-offsets.h>
#include <asm/opal.h>
#include <asm/jump_label.h>
.section ".text"

2
arch/powerpc/platforms/pseries/hvCall.S
View File

@ -7,12 +7,12 @@
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/jump_label.h>
#include <asm/hvcall.h>
#include <asm/processor.h>
#include <asm/ppc_asm.h>
#include <asm/asm-offsets.h>
#include <asm/ptrace.h>
#include <asm/jump_label.h>
.section ".text"

2
arch/powerpc/platforms/pseries/lpar.c
View File

@ -26,7 +26,7 @@
#include <linux/dma-mapping.h>
#include <linux/console.h>
#include <linux/export.h>
#include <linux/static_key.h>
#include <linux/jump_label.h>
#include <asm/processor.h>
#include <asm/mmu.h>
#include <asm/page.h>

3
arch/s390/include/asm/jump_label.h
View File

@ -1,6 +1,8 @@
#ifndef _ASM_S390_JUMP_LABEL_H
#define _ASM_S390_JUMP_LABEL_H
#ifndef __ASSEMBLY__
#include <linux/types.h>
#define JUMP_LABEL_NOP_SIZE 6
@ -39,4 +41,5 @@ struct jump_entry {
jump_label_t key;
};
#endif /* __ASSEMBLY__ */
#endif

5
arch/sparc/include/asm/jump_label.h
View File

@ -1,7 +1,7 @@
#ifndef _ASM_SPARC_JUMP_LABEL_H
#define _ASM_SPARC_JUMP_LABEL_H
#ifdef __KERNEL__
#ifndef __ASSEMBLY__
#include <linux/types.h>
@ -22,8 +22,6 @@ l_yes:
return true;
}
#endif /* __KERNEL__ */
typedef u32 jump_label_t;
struct jump_entry {
@ -32,4 +30,5 @@ struct jump_entry {
jump_label_t key;
};
#endif /* __ASSEMBLY__ */
#endif

5
arch/x86/include/asm/jump_label.h
View File

@ -1,7 +1,7 @@
#ifndef _ASM_X86_JUMP_LABEL_H
#define _ASM_X86_JUMP_LABEL_H
#ifdef __KERNEL__
#ifndef __ASSEMBLY__
#include <linux/stringify.h>
#include <linux/types.h>
@ -30,8 +30,6 @@ l_yes:
return true;
}
#endif /* __KERNEL__ */
#ifdef CONFIG_X86_64
typedef u64 jump_label_t;
#else
@ -44,4 +42,5 @@ struct jump_entry {
jump_label_t key;
};
#endif /* __ASSEMBLY__ */
#endif

16
include/linux/compiler.h
View File

@ -192,29 +192,16 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
#include <uapi/linux/types.h>
static __always_inline void data_access_exceeds_word_size(void)
#ifdef __compiletime_warning
__compiletime_warning("data access exceeds word size and won't be atomic")
#endif
;
static __always_inline void data_access_exceeds_word_size(void)
{
}
static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
{
switch (size) {
case 1: *(__u8 *)res = *(volatile __u8 *)p; break;
case 2: *(__u16 *)res = *(volatile __u16 *)p; break;
case 4: *(__u32 *)res = *(volatile __u32 *)p; break;
#ifdef CONFIG_64BIT
case 8: *(__u64 *)res = *(volatile __u64 *)p; break;
#endif
default:
barrier();
__builtin_memcpy((void *)res, (const void *)p, size);
data_access_exceeds_word_size();
barrier();
}
}
@ -225,13 +212,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
#ifdef CONFIG_64BIT
case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
#endif
default:
barrier();
__builtin_memcpy((void *)p, (const void *)res, size);
data_access_exceeds_word_size();
barrier();
}
}

21
include/linux/jump_label.h
View File

@ -45,6 +45,12 @@
* same as using STATIC_KEY_INIT_FALSE.
*/
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
# define HAVE_JUMP_LABEL
#endif
#ifndef __ASSEMBLY__
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/bug.h>
@ -55,7 +61,7 @@ extern bool static_key_initialized;
"%s used before call to jump_label_init", \
__func__)
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
#ifdef HAVE_JUMP_LABEL
struct static_key {
atomic_t enabled;
@ -66,13 +72,18 @@ struct static_key {
#endif
};
# include <asm/jump_label.h>
# define HAVE_JUMP_LABEL
#else
struct static_key {
atomic_t enabled;
};
#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
#endif /* HAVE_JUMP_LABEL */
#endif /* __ASSEMBLY__ */
#ifdef HAVE_JUMP_LABEL
#include <asm/jump_label.h>
#endif
#ifndef __ASSEMBLY__
enum jump_label_type {
JUMP_LABEL_DISABLE = 0,
@ -203,3 +214,5 @@ static inline bool static_key_enabled(struct static_key *key)
}
#endif /* _LINUX_JUMP_LABEL_H */
#endif /* __ASSEMBLY__ */

6
include/linux/seqlock.h
View File

@ -108,7 +108,7 @@ static inline unsigned __read_seqcount_begin(const seqcount_t *s)
unsigned ret;
repeat:
ret = ACCESS_ONCE(s->sequence);
ret = READ_ONCE(s->sequence);
if (unlikely(ret & 1)) {
cpu_relax();
goto repeat;
@ -127,7 +127,7 @@ repeat:
*/
static inline unsigned raw_read_seqcount(const seqcount_t *s)
{
unsigned ret = ACCESS_ONCE(s->sequence);
unsigned ret = READ_ONCE(s->sequence);
smp_rmb();
return ret;
}
@ -179,7 +179,7 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s)
*/
static inline unsigned raw_seqcount_begin(const seqcount_t *s)
{
unsigned ret = ACCESS_ONCE(s->sequence);
unsigned ret = READ_ONCE(s->sequence);
smp_rmb();
return ret & ~1;
}

2
kernel/futex.c
View File

@ -900,7 +900,7 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
if (!p)
return -ESRCH;
if (!p->mm) {
if (unlikely(p->flags & PF_KTHREAD)) {
put_task_struct(p);
return -EPERM;
}

6
kernel/locking/mcs_spinlock.h
View File

@ -78,7 +78,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
*/
return;
}
ACCESS_ONCE(prev->next) = node;
WRITE_ONCE(prev->next, node);
/* Wait until the lock holder passes the lock down. */
arch_mcs_spin_lock_contended(&node->locked);
@ -91,7 +91,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
static inline
void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
{
struct mcs_spinlock *next = ACCESS_ONCE(node->next);
struct mcs_spinlock *next = READ_ONCE(node->next);
if (likely(!next)) {
/*
@ -100,7 +100,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
if (likely(cmpxchg(lock, node, NULL) == node))
return;
/* Wait until the next pointer is set */
while (!(next = ACCESS_ONCE(node->next)))
while (!(next = READ_ONCE(node->next)))
cpu_relax_lowlatency();
}

51
kernel/locking/mutex.c
View File

@ -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 +217,35 @@ ww_mutex_set_context_slowpath(struct ww_mutex *lock,
}
#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 = true;
rcu_read_lock();
while (owner_running(lock, owner)) {
if (need_resched())
while (lock->owner == owner) {
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking lock->owner still matches owner. If that fails,
* owner might point to freed 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;
}
/*
@ -269,7 +260,7 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
return 0;
rcu_read_lock();
owner = ACCESS_ONCE(lock->owner);
owner = READ_ONCE(lock->owner);
if (owner)
retval = owner->on_cpu;
rcu_read_unlock();
@ -343,7 +334,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
* As such, when deadlock detection needs to be
* performed the optimistic spinning cannot be done.
*/
if (ACCESS_ONCE(ww->ctx))
if (READ_ONCE(ww->ctx))
break;
}
@ -351,7 +342,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
* If there's an owner, wait for it to either
* release the lock or go to sleep.
*/
owner = ACCESS_ONCE(lock->owner);
owner = READ_ONCE(lock->owner);
if (owner && !mutex_spin_on_owner(lock, owner))
break;
@ -490,7 +481,7 @@ static inline int __sched
__ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
{
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
if (!hold_ctx)
return 0;

14
kernel/locking/osq_lock.c
View File

@ -98,7 +98,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
prev = decode_cpu(old);
node->prev = prev;
ACCESS_ONCE(prev->next) = node;
WRITE_ONCE(prev->next, node);
/*
* Normally @prev is untouchable after the above store; because at that
@ -109,7 +109,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
* cmpxchg in an attempt to undo our queueing.
*/
while (!ACCESS_ONCE(node->locked)) {
while (!READ_ONCE(node->locked)) {
/*
* If we need to reschedule bail... so we can block.
*/
@ -148,7 +148,7 @@ unqueue:
* Or we race against a concurrent unqueue()'s step-B, in which
* case its step-C will write us a new @node->prev pointer.
*/
prev = ACCESS_ONCE(node->prev);
prev = READ_ONCE(node->prev);
}
/*
@ -170,8 +170,8 @@ unqueue:
* it will wait in Step-A.
*/
ACCESS_ONCE(next->prev) = prev;
ACCESS_ONCE(prev->next) = next;
WRITE_ONCE(next->prev, prev);
WRITE_ONCE(prev->next, next);
return false;
}
@ -193,11 +193,11 @@ void osq_unlock(struct optimistic_spin_queue *lock)
node = this_cpu_ptr(&osq_node);
next = xchg(&node->next, NULL);
if (next) {
ACCESS_ONCE(next->locked) = 1;
WRITE_ONCE(next->locked, 1);
return;
}
next = osq_wait_next(lock, node, NULL);
if (next)
ACCESS_ONCE(next->locked) = 1;
WRITE_ONCE(next->locked, 1);
}

2
kernel/locking/rtmutex.c
View File

@ -349,7 +349,7 @@ static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
*
* @task: the task owning the mutex (owner) for which a chain walk is
* probably needed
* @deadlock_detect: do we have to carry out deadlock detection?
* @chwalk: do we have to carry out deadlock detection?
* @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
* things for a task that has just got its priority adjusted, and
* is waiting on a mutex)

7
kernel/locking/rwsem-spinlock.c
View File

@ -85,6 +85,13 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
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);

98
kernel/locking/rwsem-xadd.c
View File

@ -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 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type)
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 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
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;
}
@ -270,15 +279,17 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
*/
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
{
long old, count = ACCESS_ONCE(sem->count);
long old, count = READ_ONCE(sem->count);
while (true) {
if (!(count == 0 || count == RWSEM_WAITING_BIAS))
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;
}
@ -287,60 +298,67 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
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;
owner = READ_ONCE(sem->owner);
if (!owner) {
long count = READ_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;
}
ret = owner->on_cpu;
done:
rcu_read_unlock();
/*
* 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;
}
static inline bool owner_running(struct rw_semaphore *sem,
struct task_struct *owner)
{
if (sem->owner != owner)
return false;
/*
* Ensure we emit the owner->on_cpu, dereference _after_ checking
* sem->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;
return ret;
}
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;
while (sem->owner == owner) {
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking sem->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();
/* abort spinning when need_resched or owner is not running */
if (!owner->on_cpu || 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)
@ -358,7 +376,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
goto done;
while (true) {
owner = ACCESS_ONCE(sem->owner);
owner = READ_ONCE(sem->owner);
if (owner && !rwsem_spin_on_owner(sem, owner))
break;
@ -432,7 +450,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
/* we're now waiting on the lock, but no longer actively locking */
if (waiting) {
count = ACCESS_ONCE(sem->count);
count = READ_ONCE(sem->count);
/*
* If there were already threads queued before us and there are

22
kernel/locking/rwsem.c
View File

@ -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

20
kernel/locking/rwsem.h Normal file
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@ -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

2
lib/lockref.c
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@ -18,7 +18,7 @@
#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
struct lockref old; \
BUILD_BUG_ON(sizeof(old) != 8); \
old.lock_count = ACCESS_ONCE(lockref->lock_count); \
old.lock_count = READ_ONCE(lockref->lock_count); \
while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
struct lockref new = old, prev = old; \
CODE \