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authorPaul E. McKenney <paul.mckenney@linaro.org>2011-10-07 18:22:04 +0200
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-12-11 10:31:33 -0800
commitff195cb69ba8d2af9b891be3a26db95fe1999d43 (patch)
treeb7e3071e87e8abdf998d4d6200228ef1a9c906d6 /include/linux/srcu.h
parentd8ab29f8be918b34a1ccd174569a53f0eb04b0a5 (diff)
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rcu: Warn when srcu_read_lock() is used in an extended quiescent state
Catch SRCU up to the other variants of RCU by making PROVE_RCU complain if either srcu_read_lock() or srcu_read_lock_held() are used from within RCU-idle mode. Frederic reworked this to allow for the new versions of his patches that check for extended quiescent states. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'include/linux/srcu.h')
-rw-r--r--include/linux/srcu.h36
1 files changed, 23 insertions, 13 deletions
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 58971e891f48..4e0a3d41dae3 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -28,6 +28,7 @@
#define _LINUX_SRCU_H
#include <linux/mutex.h>
+#include <linux/rcupdate.h>
struct srcu_struct_array {
int c[2];
@@ -60,18 +61,10 @@ int __init_srcu_struct(struct srcu_struct *sp, const char *name,
__init_srcu_struct((sp), #sp, &__srcu_key); \
})
-# define srcu_read_acquire(sp) \
- lock_acquire(&(sp)->dep_map, 0, 0, 2, 1, NULL, _THIS_IP_)
-# define srcu_read_release(sp) \
- lock_release(&(sp)->dep_map, 1, _THIS_IP_)
-
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
int init_srcu_struct(struct srcu_struct *sp);
-# define srcu_read_acquire(sp) do { } while (0)
-# define srcu_read_release(sp) do { } while (0)
-
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
void cleanup_srcu_struct(struct srcu_struct *sp);
@@ -90,12 +83,29 @@ long srcu_batches_completed(struct srcu_struct *sp);
* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
* this assumes we are in an SRCU read-side critical section unless it can
* prove otherwise.
+ *
+ * Note that if the CPU is in the idle loop from an RCU point of view
+ * (ie: that we are in the section between rcu_idle_enter() and
+ * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
+ * the CPU did an srcu_read_lock(). The reason for this is that RCU
+ * ignores CPUs that are in such a section, considering these as in
+ * extended quiescent state, so such a CPU is effectively never in an
+ * RCU read-side critical section regardless of what RCU primitives it
+ * invokes. This state of affairs is required --- we need to keep an
+ * RCU-free window in idle where the CPU may possibly enter into low
+ * power mode. This way we can notice an extended quiescent state to
+ * other CPUs that started a grace period. Otherwise we would delay any
+ * grace period as long as we run in the idle task.
*/
static inline int srcu_read_lock_held(struct srcu_struct *sp)
{
- if (debug_locks)
- return lock_is_held(&sp->dep_map);
- return 1;
+ if (rcu_is_cpu_idle())
+ return 0;
+
+ if (!debug_locks)
+ return 1;
+
+ return lock_is_held(&sp->dep_map);
}
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -150,7 +160,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
{
int retval = __srcu_read_lock(sp);
- srcu_read_acquire(sp);
+ rcu_lock_acquire(&(sp)->dep_map);
return retval;
}
@@ -164,7 +174,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
__releases(sp)
{
- srcu_read_release(sp);
+ rcu_lock_release(&(sp)->dep_map);
__srcu_read_unlock(sp, idx);
}