#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.
* 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 {
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; \
(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 }
.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 = \
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 *);
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);
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 */
/*
* Atomic notifier chain routines. Registration and unregistration
- * use a mutex, and call_chain is synchronized by RCU (no locks).
+ * use a spinlock, and call_chain is synchronized by RCU (no locks).
*/
/**
EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
+/*
+ * SRCU notifier chain routines. Registration and unregistration
+ * use a mutex, and call_chain is synchronized by SRCU (no locks).
+ */
+
+/**
+ * srcu_notifier_chain_register - Add notifier to an SRCU notifier chain
+ * @nh: Pointer to head of the SRCU notifier chain
+ * @n: New entry in notifier chain
+ *
+ * Adds a notifier to an SRCU notifier chain.
+ * Must be called in process context.
+ *
+ * Currently always returns zero.
+ */
+
+int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
+ struct notifier_block *n)
+{
+ int ret;
+
+ /*
+ * This code gets used during boot-up, when task switching is
+ * not yet working and interrupts must remain disabled. At
+ * such times we must not call mutex_lock().
+ */
+ if (unlikely(system_state == SYSTEM_BOOTING))
+ return notifier_chain_register(&nh->head, n);
+
+ mutex_lock(&nh->mutex);
+ ret = notifier_chain_register(&nh->head, n);
+ mutex_unlock(&nh->mutex);
+ return ret;
+}
+
+EXPORT_SYMBOL_GPL(srcu_notifier_chain_register);
+
+/**
+ * srcu_notifier_chain_unregister - Remove notifier from an SRCU notifier chain
+ * @nh: Pointer to head of the SRCU notifier chain
+ * @n: Entry to remove from notifier chain
+ *
+ * Removes a notifier from an SRCU notifier chain.
+ * Must be called from process context.
+ *
+ * Returns zero on success or %-ENOENT on failure.
+ */
+int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
+ struct notifier_block *n)
+{
+ int ret;
+
+ /*
+ * This code gets used during boot-up, when task switching is
+ * not yet working and interrupts must remain disabled. At
+ * such times we must not call mutex_lock().
+ */
+ if (unlikely(system_state == SYSTEM_BOOTING))
+ return notifier_chain_unregister(&nh->head, n);
+
+ mutex_lock(&nh->mutex);
+ ret = notifier_chain_unregister(&nh->head, n);
+ mutex_unlock(&nh->mutex);
+ synchronize_srcu(&nh->srcu);
+ return ret;
+}
+
+EXPORT_SYMBOL_GPL(srcu_notifier_chain_unregister);
+
+/**
+ * srcu_notifier_call_chain - Call functions in an SRCU notifier chain
+ * @nh: Pointer to head of the SRCU notifier chain
+ * @val: Value passed unmodified to notifier function
+ * @v: Pointer passed unmodified to notifier function
+ *
+ * Calls each function in a notifier chain in turn. The functions
+ * run in a process context, so they are allowed to block.
+ *
+ * If the return value of the notifier can be and'ed
+ * with %NOTIFY_STOP_MASK then srcu_notifier_call_chain
+ * will return immediately, with the return value of
+ * the notifier function which halted execution.
+ * Otherwise the return value is the return value
+ * of the last notifier function called.
+ */
+
+int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
+ unsigned long val, void *v)
+{
+ int ret;
+ int idx;
+
+ idx = srcu_read_lock(&nh->srcu);
+ ret = notifier_call_chain(&nh->head, val, v);
+ srcu_read_unlock(&nh->srcu, idx);
+ return ret;
+}
+
+EXPORT_SYMBOL_GPL(srcu_notifier_call_chain);
+
+/**
+ * srcu_init_notifier_head - Initialize an SRCU notifier head
+ * @nh: Pointer to head of the srcu notifier chain
+ *
+ * Unlike other sorts of notifier heads, SRCU notifier heads require
+ * dynamic initialization. Be sure to call this routine before
+ * calling any of the other SRCU notifier routines for this head.
+ *
+ * If an SRCU notifier head is deallocated, it must first be cleaned
+ * up by calling srcu_cleanup_notifier_head(). Otherwise the head's
+ * per-cpu data (used by the SRCU mechanism) will leak.
+ */
+
+void srcu_init_notifier_head(struct srcu_notifier_head *nh)
+{
+ mutex_init(&nh->mutex);
+ init_srcu_struct(&nh->srcu);
+ nh->head = NULL;
+}
+
+EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
+
/**
* register_reboot_notifier - Register function to be called at reboot time
* @nb: Info about notifier function to be called
projects / openwrt / staging / blogic.git / commitdiff