Add the function callout_init_rw() to callout facility in order to use

rwlocks in conjuction with callouts.  The function does basically what
callout_init_mtx() alredy does with the difference of using a rwlock
as extra argument.
CALLOUT_SHAREDLOCK flag can be used, now, in order to acquire the lock only
in read mode when running the callout handler.  It has no effects when used
in conjuction with mtx.

In order to implement this, underlying callout functions have been made
completely lock type-unaware, so accordingly with this, sysctl
debug.to_avg_mtxcalls is now changed in the generic
debug.to_avg_lockcalls.

Note: currently the allowed lock classes are mutexes and rwlocks because
callout handlers run in softclock swi, so they cannot sleep and they
cannot acquire sleepable locks like sx or lockmgr.

Requested by: kmacy, pjd, rwatson
Reviewed by: jhb

1 files changed, 10 insertions, 3 deletions

diff --git a/sys/sys/callout.h b/sys/sys/callout.h
index a554562..d7adeaf 100644
--- a/sys/sys/callout.h
+++ b/sys/sys/callout.h
@@ -40,7 +40,7 @@
 
 #include <sys/queue.h>
 
-struct mtx;
+struct lock_object;
 
 SLIST_HEAD(callout_list, callout);
 TAILQ_HEAD(callout_tailq, callout);
@@ -53,7 +53,7 @@ struct callout {
 	int	c_time;				/* ticks to the event */
 	void	*c_arg;				/* function argument */
 	void	(*c_func)(void *);	/* function to call */
-	struct mtx *c_mtx;			/* mutex to lock */
+	struct lock_object *c_lock;		/* lock to handle */
 	int	c_flags;			/* state of this entry */
 };
 
@@ -62,6 +62,7 @@ struct callout {
 #define	CALLOUT_PENDING		0x0004 /* callout is waiting for timeout */
 #define	CALLOUT_MPSAFE		0x0008 /* callout handler is mp safe */
 #define	CALLOUT_RETURNUNLOCKED	0x0010 /* handler returns with mtx unlocked */
+#define	CALLOUT_SHAREDLOCK	0x0020 /* callout lock held in shared mode */
 
 struct callout_handle {
 	struct callout *callout;
@@ -79,7 +80,13 @@ extern struct mtx callout_lock;
 #define	callout_deactivate(c)	((c)->c_flags &= ~CALLOUT_ACTIVE)
 #define	callout_drain(c)	_callout_stop_safe(c, 1)
 void	callout_init(struct callout *, int);
-void	callout_init_mtx(struct callout *, struct mtx *, int);
+void	_callout_init_lock(struct callout *, struct lock_object *, int);
+#define	callout_init_mtx(c, mtx, flags)					\
+	_callout_init_lock((c), ((mtx) != NULL) ? &(mtx)->lock_object :	\
+	    NULL, (flags))
+#define	callout_init_rw(c, rw, flags)					\
+	_callout_init_lock((c), ((rw) != NULL) ? &(rw)->lock_object :	\
+	   NULL, (flags))
 #define	callout_pending(c)	((c)->c_flags & CALLOUT_PENDING)
 int	callout_reset(struct callout *, int, void (*)(void *), void *);
 #define	callout_stop(c)		_callout_stop_safe(c, 0)