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Diffstat (limited to 'include/linux/notifier.h')
-rw-r--r--include/linux/notifier.h43
1 files changed, 38 insertions, 5 deletions
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 7ff386a6ae8..10a43ed0527 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -12,9 +12,10 @@
#include <linux/errno.h>
#include <linux/mutex.h>
#include <linux/rwsem.h>
+#include <linux/srcu.h>
/*
- * Notifier chains are of three types:
+ * Notifier chains are of four types:
*
* Atomic notifier chains: Chain callbacks run in interrupt/atomic
* context. Callouts are not allowed to block.
@@ -23,13 +24,27 @@
* Raw notifier chains: There are no restrictions on callbacks,
* registration, or unregistration. All locking and protection
* must be provided by the caller.
+ * SRCU notifier chains: A variant of blocking notifier chains, with
+ * the same restrictions.
*
* atomic_notifier_chain_register() may be called from an atomic context,
- * but blocking_notifier_chain_register() must be called from a process
- * context. Ditto for the corresponding _unregister() routines.
+ * but blocking_notifier_chain_register() and srcu_notifier_chain_register()
+ * must be called from a process context. Ditto for the corresponding
+ * _unregister() routines.
*
- * atomic_notifier_chain_unregister() and blocking_notifier_chain_unregister()
- * _must not_ be called from within the call chain.
+ * atomic_notifier_chain_unregister(), blocking_notifier_chain_unregister(),
+ * and srcu_notifier_chain_unregister() _must not_ be called from within
+ * the call chain.
+ *
+ * SRCU notifier chains are an alternative form of blocking notifier chains.
+ * They use SRCU (Sleepable Read-Copy Update) instead of rw-semaphores for
+ * protection of the chain links. This means there is _very_ low overhead
+ * in srcu_notifier_call_chain(): no cache bounces and no memory barriers.
+ * As compensation, srcu_notifier_chain_unregister() is rather expensive.
+ * SRCU notifier chains should be used when the chain will be called very
+ * often but notifier_blocks will seldom be removed. Also, SRCU notifier
+ * chains are slightly more difficult to use because they require special
+ * runtime initialization.
*/
struct notifier_block {
@@ -52,6 +67,12 @@ struct raw_notifier_head {
struct notifier_block *head;
};
+struct srcu_notifier_head {
+ struct mutex mutex;
+ struct srcu_struct srcu;
+ struct notifier_block *head;
+};
+
#define ATOMIC_INIT_NOTIFIER_HEAD(name) do { \
spin_lock_init(&(name)->lock); \
(name)->head = NULL; \
@@ -64,6 +85,11 @@ struct raw_notifier_head {
(name)->head = NULL; \
} while (0)
+/* srcu_notifier_heads must be initialized and cleaned up dynamically */
+extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
+#define srcu_cleanup_notifier_head(name) \
+ cleanup_srcu_struct(&(name)->srcu);
+
#define ATOMIC_NOTIFIER_INIT(name) { \
.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
.head = NULL }
@@ -72,6 +98,7 @@ struct raw_notifier_head {
.head = NULL }
#define RAW_NOTIFIER_INIT(name) { \
.head = NULL }
+/* srcu_notifier_heads cannot be initialized statically */
#define ATOMIC_NOTIFIER_HEAD(name) \
struct atomic_notifier_head name = \
@@ -91,6 +118,8 @@ extern int blocking_notifier_chain_register(struct blocking_notifier_head *,
struct notifier_block *);
extern int raw_notifier_chain_register(struct raw_notifier_head *,
struct notifier_block *);
+extern int srcu_notifier_chain_register(struct srcu_notifier_head *,
+ struct notifier_block *);
extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *,
struct notifier_block *);
@@ -98,6 +127,8 @@ extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *,
struct notifier_block *);
extern int raw_notifier_chain_unregister(struct raw_notifier_head *,
struct notifier_block *);
+extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *,
+ struct notifier_block *);
extern int atomic_notifier_call_chain(struct atomic_notifier_head *,
unsigned long val, void *v);
@@ -105,6 +136,8 @@ extern int blocking_notifier_call_chain(struct blocking_notifier_head *,
unsigned long val, void *v);
extern int raw_notifier_call_chain(struct raw_notifier_head *,
unsigned long val, void *v);
+extern int srcu_notifier_call_chain(struct srcu_notifier_head *,
+ unsigned long val, void *v);
#define NOTIFY_DONE 0x0000 /* Don't care */
#define NOTIFY_OK 0x0001 /* Suits me */