Page MenuHomeFreeBSD
Files F144095524

D21254.id60756.diff
No OneTemporary
Actions

D21254.id60756.diff
View Options

Index: sys/kern/kern_synch.c
===================================================================
--- sys/kern/kern_synch.c
+++ sys/kern/kern_synch.c
@@ -52,6 +52,7 @@
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
+#include <sys/refcount.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
@@ -333,6 +334,36 @@
(flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags));
}
+/*
+ * Wait for a refcount wakeup. This does not guarantee that the ref is still
+ * zero on return and may be subject to transient wakeups. Callers wanting
+ * a precise answer should use refcount_wait().
+ */
+void
+refcount_sleep(volatile u_int *count, const char *wmesg, int pri)
+{
+ void *wchan;
+ u_int old;
+
+ if (REFCOUNT_COUNT(*count) == 0)
+ return;
+ wchan = __DEVOLATILE(void *, count);
+ sleepq_lock(wchan);
+ old = *count;
+ for (;;) {
+ if (REFCOUNT_COUNT(old) == 0) {
+ sleepq_release(wchan);
+ return;
+ }
+ if (old & REFCOUNT_WAITER)
+ break;
+ if (atomic_fcmpset_int(count, &old, old | REFCOUNT_WAITER))
+ break;
+ }
+ sleepq_add(wchan, NULL, wmesg, 0, 0);
+ sleepq_wait(wchan, pri);
+}
+
/*
* Make all threads sleeping on the specified identifier runnable.
*/
Index: sys/sys/refcount.h
===================================================================
--- sys/sys/refcount.h
+++ sys/sys/refcount.h
@@ -39,8 +39,11 @@
#define KASSERT(exp, msg) /* */
#endif
-#define REFCOUNT_SATURATED(val) (((val) & (1U << 31)) != 0)
-#define REFCOUNT_SATURATION_VALUE (3U << 30)
+#define REFCOUNT_WAITER (1 << 31) /* Refcount has waiter. */
+#define REFCOUNT_SATURATION_VALUE (3U << 29)
+
+#define REFCOUNT_SATURATED(val) (((val) & (1U << 30)) != 0)
+#define REFCOUNT_COUNT(x) ((x) & ~REFCOUNT_WAITER)
/*
* Attempt to handle reference count overflow and underflow. Force the counter
@@ -76,6 +79,17 @@
_refcount_update_saturated(count);
}
+static __inline void
+refcount_acquiren(volatile u_int *count, u_int n)
+{
+
+ u_int old;
+
+ old = atomic_fetchadd_int(count, n);
+ if (__predict_false(REFCOUNT_SATURATED(old)))
+ _refcount_update_saturated(count);
+}
+
static __inline __result_use_check bool
refcount_acquire_checked(volatile u_int *count)
{
@@ -91,13 +105,19 @@
}
static __inline bool
-refcount_release(volatile u_int *count)
+refcount_releasen(volatile u_int *count, u_int n)
{
u_int old;
+ u_int waiter;
atomic_thread_fence_rel();
- old = atomic_fetchadd_int(count, -1);
- if (__predict_false(old == 0 || REFCOUNT_SATURATED(old))) {
+ old = atomic_fetchadd_int(count, -n);
+ waiter = old & REFCOUNT_WAITER;
+ old = REFCOUNT_COUNT(old);
+ if (old > n)
+ return (false);
+
+ if (__predict_false(n > old || REFCOUNT_SATURATED(old))) {
/*
* Avoid multiple destructor invocations if underflow occurred.
* This is not perfect since the memory backing the containing
@@ -106,8 +126,14 @@
_refcount_update_saturated(count);
return (false);
}
- if (old > 1)
- return (false);
+
+ /*
+ * Attempt to atomically clear the waiter bit. Wakeup waiters
+ * if we are successful.
+ */
+ if (waiter != 0 &&
+ atomic_cmpset_int(count, REFCOUNT_WAITER, 0))
+ wakeup(__DEVOLATILE(u_int *, count));
/*
* Last reference. Signal the user to call the destructor.
@@ -119,6 +145,23 @@
return (true);
}
+static __inline bool
+refcount_release(volatile u_int *count)
+{
+
+ return (refcount_releasen(count, 1));
+}
+
+void refcount_sleep(volatile u_int *count, const char *wmesg, int prio);
+
+static __inline void
+refcount_wait(volatile u_int *count, const char *wmesg, int prio)
+{
+
+ while (*count != 0)
+ refcount_sleep(count, wmesg, prio);
+}
+
/*
* This functions returns non-zero if the refcount was
* incremented. Else zero is returned.
@@ -130,7 +173,7 @@
old = *count;
for (;;) {
- if (old == 0)
+ if (REFCOUNT_COUNT(old) == 0)
return (false);
if (__predict_false(REFCOUNT_SATURATED(old)))
return (true);
@@ -146,7 +189,7 @@
old = *count;
for (;;) {
- if (old == 1)
+ if (REFCOUNT_COUNT(old) == 1)
return (false);
if (__predict_false(REFCOUNT_SATURATED(old)))
return (true);

File Metadata

Mime Type
text/plain
Expires
Thu, Feb 5, 4:24 PM (2 h, 18 m)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
28443066
Default Alt Text
D21254.id60756.diff (4 KB)

Event Timeline