Author: ed
Date: Sun Jun 16 09:30:35 2013
New Revision: 251803
URL: http://svnweb.freebsd.org/changeset/base/251803
Log:
Change callout use counter to use C11 atomics.
In order to get some coverage of C11 atomics in kernelspace, switch at
least one piece of code in kernelspace to use C11 atomics instead of
<machine/atomic.h>.
While there, slightly improve the code by adding an assertion to prevent
the use count from going negative.
Modified:
head/sys/kern/kern_event.c
Modified: head/sys/kern/kern_event.c
==============================================================================
--- head/sys/kern/kern_event.c Sun Jun 16 07:18:07 2013 (r251802)
+++ head/sys/kern/kern_event.c Sun Jun 16 09:30:35 2013 (r251803)
@@ -47,6 +47,7 @@ __FBSDID("$FreeBSD$");
#include <sys/fcntl.h>
#include <sys/kthread.h>
#include <sys/selinfo.h>
+#include <sys/stdatomic.h>
#include <sys/queue.h>
#include <sys/event.h>
#include <sys/eventvar.h>
@@ -182,9 +183,9 @@ static struct filterops user_filtops = {
};
static uma_zone_t knote_zone;
-static int kq_ncallouts = 0;
-static int kq_calloutmax = (4 * 1024);
-SYSCTL_INT(_kern, OID_AUTO, kq_calloutmax, CTLFLAG_RW,
+static atomic_uint kq_ncallouts = ATOMIC_VAR_INIT(0);
+static unsigned int kq_calloutmax = 4 * 1024;
+SYSCTL_UINT(_kern, OID_AUTO, kq_calloutmax, CTLFLAG_RW,
&kq_calloutmax, 0, "Maximum number of callouts allocated for kqueue");
/* XXX - ensure not KN_INFLUX?? */
@@ -549,13 +550,15 @@ static int
filt_timerattach(struct knote *kn)
{
struct callout *calloutp;
+ unsigned int ncallouts;
- atomic_add_int(&kq_ncallouts, 1);
-
- if (kq_ncallouts >= kq_calloutmax) {
- atomic_add_int(&kq_ncallouts, -1);
- return (ENOMEM);
- }
+ ncallouts = atomic_load_explicit(&kq_ncallouts, memory_order_relaxed);
+ do {
+ if (ncallouts >= kq_calloutmax)
+ return (ENOMEM);
+ } while (!atomic_compare_exchange_weak_explicit(&kq_ncallouts,
+ &ncallouts, ncallouts + 1, memory_order_relaxed,
+ memory_order_relaxed));
kn->kn_flags |= EV_CLEAR; /* automatically set */
kn->kn_status &= ~KN_DETACHED; /* knlist_add usually sets it */
@@ -573,11 +576,13 @@ static void
filt_timerdetach(struct knote *kn)
{
struct callout *calloutp;
+ unsigned int old;
calloutp = (struct callout *)kn->kn_hook;
callout_drain(calloutp);
free(calloutp, M_KQUEUE);
- atomic_add_int(&kq_ncallouts, -1);
+ old = atomic_fetch_sub_explicit(&kq_ncallouts, 1, memory_order_relaxed);
+ KASSERT(old > 0, ("Number of callouts cannot become negative"));
kn->kn_status |= KN_DETACHED; /* knlist_remove usually clears it */
}
_______________________________________________
svn-src-all@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/svn-src-all
To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
