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Revert "rwsem-rt: Do not allow readers to nest" 

This behaviour is required by cpufreq and its logic is "okay": It does a
read_lock followed by a try_read_lock.
Lockdep warns if one try a read_lock twice in -RT and vanilla so it
should be good. We still only allow multiple readers as long as it is in
the same process.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Sebastian Andrzej Siewior 2015-02-25 12:16:43 +01:00 committed by Alibek Omarov
parent b54201289c
commit d12e92f871
2 changed files with 24 additions and 6 deletions
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1
include/linux/rwsem_rt.h
View File

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

29
kernel/locking/rt.c
View File

@ -322,7 +322,8 @@ EXPORT_SYMBOL(rt_up_write);
void rt_up_read(struct rw_semaphore *rwsem)
{
rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
rt_mutex_unlock(&rwsem->lock);
if (--rwsem->read_depth == 0)
rt_mutex_unlock(&rwsem->lock);
}
EXPORT_SYMBOL(rt_up_read);
@ -333,6 +334,7 @@ EXPORT_SYMBOL(rt_up_read);
void rt_downgrade_write(struct rw_semaphore *rwsem)
{
BUG_ON(rt_mutex_owner(&rwsem->lock) != current);
rwsem->read_depth = 1;
}
EXPORT_SYMBOL(rt_downgrade_write);
@ -370,12 +372,23 @@ EXPORT_SYMBOL(rt_down_write_nested_lock);
int rt_down_read_trylock(struct rw_semaphore *rwsem)
{
int ret;
struct rt_mutex *lock = &rwsem->lock;
int ret = 1;
ret = rt_mutex_trylock(&rwsem->lock);
if (ret)
/*
* recursive read locks succeed when current owns the rwsem,
* 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_);
}
return ret;
}
EXPORT_SYMBOL(rt_down_read_trylock);
@ -383,7 +396,10 @@ EXPORT_SYMBOL(rt_down_read_trylock);
static void __rt_down_read(struct rw_semaphore *rwsem, int subclass)
{
rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
rt_mutex_lock(&rwsem->lock);
if (rt_mutex_owner(&rwsem->lock) != current)
rt_mutex_lock(&rwsem->lock);
rwsem->read_depth++;
}
void rt_down_read(struct rw_semaphore *rwsem)
@ -408,6 +424,7 @@ void __rt_rwsem_init(struct rw_semaphore *rwsem, const char *name,
debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem));
lockdep_init_map(&rwsem->dep_map, name, key, 0);
#endif
rwsem->read_depth = 0;
rwsem->lock.save_state = 0;
}
EXPORT_SYMBOL(__rt_rwsem_init);