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rwsem-rt: Do not allow readers to nest 

The readers of mainline rwsems are not allowed to nest, the rwsems in the
PREEMPT_RT kernel should not nest either.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
This commit is contained in:
Steven Rostedt (Red Hat) 2014-05-02 10:53:30 +02:00 committed by Alibek Omarov
parent 6c23aac84d
commit d5af4a6a85
2 changed files with 6 additions and 24 deletions
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1
include/linux/rwsem_rt.h
View File

@ -20,7 +20,6 @@
struct rw_semaphore { struct rw_semaphore {
struct rt_mutex lock; struct rt_mutex lock;
int read_depth;
#ifdef CONFIG_DEBUG_LOCK_ALLOC #ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map; struct lockdep_map dep_map;
#endif #endif

29
kernel/locking/rt.c
View File

@ -316,8 +316,7 @@ EXPORT_SYMBOL(rt_up_write);
void rt_up_read(struct rw_semaphore *rwsem) void rt_up_read(struct rw_semaphore *rwsem)
{ {
rwsem_release(&rwsem->dep_map, 1, _RET_IP_); rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
if (--rwsem->read_depth == 0) rt_mutex_unlock(&rwsem->lock);
rt_mutex_unlock(&rwsem->lock);
} }
EXPORT_SYMBOL(rt_up_read); EXPORT_SYMBOL(rt_up_read);
@ -328,7 +327,6 @@ EXPORT_SYMBOL(rt_up_read);
void rt_downgrade_write(struct rw_semaphore *rwsem) void rt_downgrade_write(struct rw_semaphore *rwsem)
{ {
BUG_ON(rt_mutex_owner(&rwsem->lock) != current); BUG_ON(rt_mutex_owner(&rwsem->lock) != current);
rwsem->read_depth = 1;
} }
EXPORT_SYMBOL(rt_downgrade_write); EXPORT_SYMBOL(rt_downgrade_write);
@ -358,23 +356,12 @@ EXPORT_SYMBOL(rt_down_write_nested);
int rt_down_read_trylock(struct rw_semaphore *rwsem) int rt_down_read_trylock(struct rw_semaphore *rwsem)
{ {
struct rt_mutex *lock = &rwsem->lock; int ret;
int ret = 1;
/* ret = rt_mutex_trylock(&rwsem->lock);
* recursive read locks succeed when current owns the rwsem, if (ret)
* but not when read_depth == 0 which means that the rwsem is
* write locked.
*/
if (rt_mutex_owner(lock) != current)
ret = rt_mutex_trylock(&rwsem->lock);
else if (!rwsem->read_depth)
ret = 0;
if (ret) {
rwsem->read_depth++;
rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
}
return ret; return ret;
} }
EXPORT_SYMBOL(rt_down_read_trylock); EXPORT_SYMBOL(rt_down_read_trylock);
@ -384,10 +371,7 @@ static void __rt_down_read(struct rw_semaphore *rwsem, int subclass)
struct rt_mutex *lock = &rwsem->lock; struct rt_mutex *lock = &rwsem->lock;
rwsem_acquire_read(&rwsem->dep_map, subclass, 0, _RET_IP_); rwsem_acquire_read(&rwsem->dep_map, subclass, 0, _RET_IP_);
rt_mutex_lock(&rwsem->lock);
if (rt_mutex_owner(lock) != current)
rt_mutex_lock(&rwsem->lock);
rwsem->read_depth++;
} }
void rt_down_read(struct rw_semaphore *rwsem) void rt_down_read(struct rw_semaphore *rwsem)
@ -412,7 +396,6 @@ void __rt_rwsem_init(struct rw_semaphore *rwsem, const char *name,
debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem)); debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem));
lockdep_init_map(&rwsem->dep_map, name, key, 0); lockdep_init_map(&rwsem->dep_map, name, key, 0);
#endif #endif
rwsem->read_depth = 0;
rwsem->lock.save_state = 0; rwsem->lock.save_state = 0;
} }
EXPORT_SYMBOL(__rt_rwsem_init); EXPORT_SYMBOL(__rt_rwsem_init);