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Subject[PATCH RT 1/2] rwsem-rt: Do not allow readers to nest
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

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>
---
include/linux/rwsem_rt.h | 1 -
kernel/rt.c | 37 ++++++++-----------------------------
2 files changed, 8 insertions(+), 30 deletions(-)

diff --git a/include/linux/rwsem_rt.h b/include/linux/rwsem_rt.h
index e94d945..a81151c 100644
--- a/include/linux/rwsem_rt.h
+++ b/include/linux/rwsem_rt.h
@@ -20,7 +20,6 @@

struct rw_semaphore {
struct rt_mutex lock;
- int read_depth;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
diff --git a/kernel/rt.c b/kernel/rt.c
index 5d17727..bb72347 100644
--- a/kernel/rt.c
+++ b/kernel/rt.c
@@ -316,10 +316,8 @@ EXPORT_SYMBOL(rt_up_write);

void rt_up_read(struct rw_semaphore *rwsem)
{
- if (--rwsem->read_depth == 0) {
- rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
- rt_mutex_unlock(&rwsem->lock);
- }
+ rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
+ rt_mutex_unlock(&rwsem->lock);
}
EXPORT_SYMBOL(rt_up_read);

@@ -330,7 +328,6 @@ 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);

@@ -367,37 +364,20 @@ void rt_down_write_nested_lock(struct rw_semaphore *rwsem,

int rt_down_read_trylock(struct rw_semaphore *rwsem)
{
- struct rt_mutex *lock = &rwsem->lock;
- int ret = 1;
-
- /*
- * 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);
- if (ret)
- rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
- } else if (!rwsem->read_depth) {
- ret = 0;
- }
+ int ret;

+ ret = rt_mutex_trylock(&rwsem->lock);
if (ret)
- rwsem->read_depth++;
+ rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
+
return ret;
}
EXPORT_SYMBOL(rt_down_read_trylock);

static void __rt_down_read(struct rw_semaphore *rwsem, int subclass)
{
- struct rt_mutex *lock = &rwsem->lock;
-
- if (rt_mutex_owner(lock) != current) {
- rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
- rt_mutex_lock(&rwsem->lock);
- }
- rwsem->read_depth++;
+ rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
+ rt_mutex_lock(&rwsem->lock);
}

void rt_down_read(struct rw_semaphore *rwsem)
@@ -422,7 +402,6 @@ 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);
--
1.8.5.3



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