[PATCH RT 1/2] rwsem-rt: Do not allow readers to nest

[Steven Rostedt]

From: "Steven Rostedt (Red Hat)" <rost...@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 <rost...@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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