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Index: sys/vm/vm_page.h
===================================================================
--- sys/vm/vm_page.h
+++ sys/vm/vm_page.h
@@ -100,7 +100,8 @@
* field and is described in detail below.
*
* The following annotations are possible:
- * (A) the field is atomic and may require additional synchronization.
+ * (A) the field must be accessed using atomic(9) and may require
+ * additional synchronization.
* (B) the page busy lock.
* (C) the field is immutable.
* (F) the per-domain lock for the free queues
@@ -243,8 +244,8 @@
vm_paddr_t phys_addr; /* physical address of page (C) */
struct md_page md; /* machine dependent stuff */
u_int ref_count; /* page references (A) */
- volatile u_int busy_lock; /* busy owners lock */
- union vm_page_astate a; /* state accessed atomically */
+ u_int busy_lock; /* busy owners lock (A) */
+ union vm_page_astate a; /* state accessed atomically (A) */
uint8_t order; /* index of the buddy queue (F) */
uint8_t pool; /* vm_phys freepool index (F) */
uint8_t flags; /* page PG_* flags (P) */
@@ -701,6 +702,8 @@
void vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line);
#endif
+#define vm_page_busy_fetch(m) atomic_load_int(&(m)->busy_lock)
+
#define vm_page_assert_busied(m) \
KASSERT(vm_page_busied(m), \
("vm_page_assert_busied: page %p not busy @ %s:%d", \
@@ -712,7 +715,7 @@
(m), __FILE__, __LINE__))
#define vm_page_assert_unbusied(m) \
- KASSERT((m->busy_lock & ~VPB_BIT_WAITERS) != \
+ KASSERT((vm_page_busy_fetch(m) & ~VPB_BIT_WAITERS) != \
VPB_CURTHREAD_EXCLUSIVE, \
("vm_page_assert_xbusied: page %p busy_lock %#x owned" \
" by me @ %s:%d", \
@@ -725,7 +728,7 @@
} while (0)
#define vm_page_assert_xbusied(m) do { \
vm_page_assert_xbusied_unchecked(m); \
- KASSERT((m->busy_lock & ~VPB_BIT_WAITERS) == \
+ KASSERT((vm_page_busy_fetch(m) & ~VPB_BIT_WAITERS) == \
VPB_CURTHREAD_EXCLUSIVE, \
("vm_page_assert_xbusied: page %p busy_lock %#x not owned" \
" by me @ %s:%d", \
@@ -733,7 +736,7 @@
} while (0)
#define vm_page_busied(m) \
- ((m)->busy_lock != VPB_UNBUSIED)
+ (vm_page_busy_fetch(m) != VPB_UNBUSIED)
#define vm_page_sbusy(m) do { \
if (!vm_page_trysbusy(m)) \
@@ -742,10 +745,10 @@
} while (0)
#define vm_page_xbusied(m) \
- (((m)->busy_lock & VPB_SINGLE_EXCLUSIVE) != 0)
+ ((vm_page_busy_fetch(m) & VPB_SINGLE_EXCLUSIVE) != 0)
#define vm_page_busy_freed(m) \
- ((m)->busy_lock == VPB_FREED)
+ (vm_page_busy_fetch(m) == VPB_FREED)
#define vm_page_xbusy(m) do { \
if (!vm_page_tryxbusy(m)) \
@@ -771,12 +774,17 @@
void vm_page_assert_pga_writeable(vm_page_t m, uint16_t bits);
#define VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits) \
vm_page_assert_pga_writeable(m, bits)
+/*
+ * Claim ownership of a page's xbusy state. In non-INVARIANTS kernels this
+ * operation is a no-op since ownership is not tracked. In particular
+ * this macro does not provide any synchronization with the previous owner.
+ */
#define vm_page_xbusy_claim(m) do { \
u_int _busy_lock; \
\
vm_page_assert_xbusied_unchecked((m)); \
do { \
- _busy_lock = atomic_load_int(&(m)->busy_lock); \
+ _busy_lock = vm_page_busy_fetch(m); \
} while (!atomic_cmpset_int(&(m)->busy_lock, _busy_lock, \
(_busy_lock & VPB_BIT_FLAGMASK) | VPB_CURTHREAD_EXCLUSIVE)); \
} while (0)
Index: sys/vm/vm_page.c
===================================================================
--- sys/vm/vm_page.c
+++ sys/vm/vm_page.c
@@ -908,7 +908,7 @@
vm_page_assert_xbusied(m);
- x = m->busy_lock;
+ x = vm_page_busy_fetch(m);
for (;;) {
if (atomic_fcmpset_rel_int(&m->busy_lock,
&x, VPB_SHARERS_WORD(1)))
@@ -931,7 +931,7 @@
vm_page_assert_sbusied(m);
- x = m->busy_lock;
+ x = vm_page_busy_fetch(m);
ce = VPB_CURTHREAD_EXCLUSIVE;
for (;;) {
if (VPB_SHARERS(x) > 1)
@@ -955,7 +955,7 @@
{
u_int x;
- x = m->busy_lock;
+ x = vm_page_busy_fetch(m);
return ((x & VPB_BIT_SHARED) != 0 && x != VPB_UNBUSIED);
}
@@ -971,7 +971,7 @@
vm_page_assert_sbusied(m);
- x = m->busy_lock;
+ x = vm_page_busy_fetch(m);
for (;;) {
KASSERT(x != VPB_FREED,
("vm_page_sunbusy: Unlocking freed page."));
@@ -1072,7 +1072,7 @@
xsleep = (allocflags & (VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY)) != 0;
sleepq_lock(m);
- x = atomic_load_int(&m->busy_lock);
+ x = vm_page_busy_fetch(m);
do {
/*
* If the page changes objects or becomes unlocked we can
@@ -1110,7 +1110,7 @@
u_int x;
obj = m->object;
- x = m->busy_lock;
+ x = vm_page_busy_fetch(m);
for (;;) {
if ((x & VPB_BIT_SHARED) == 0)
return (0);
@@ -1146,7 +1146,7 @@
{
vm_object_t obj;
- if (atomic_cmpset_acq_int(&(m)->busy_lock, VPB_UNBUSIED,
+ if (atomic_cmpset_acq_int(&m->busy_lock, VPB_UNBUSIED,
VPB_CURTHREAD_EXCLUSIVE) == 0)
return (0);
@@ -1354,7 +1354,7 @@
* have shown that deactivating the page is usually the best choice,
* unless the page is wanted by another thread.
*/
- if ((m->busy_lock & VPB_BIT_WAITERS) != 0)
+ if ((vm_page_busy_fetch(m) & VPB_BIT_WAITERS) != 0)
vm_page_activate(m);
else
vm_page_deactivate(m);
@@ -1714,7 +1714,7 @@
{
u_int x;
- x = atomic_load_int(&m->busy_lock);
+ x = vm_page_busy_fetch(m);
for (;;) {
if (x == VPB_FREED)
break;

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