4 * Copyright (c) 2003,2004,2010 The DragonFly Project. All rights reserved.
6 * This code is derived from software contributed to The DragonFly Project
7 * by Matthew Dillon <dillon@backplane.com> and David Xu <davidxu@freebsd.org>
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10 * modification, are permitted provided that the following conditions
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36 * $DragonFly: src/sys/kern/kern_umtx.c,v 1.9 2008/05/09 07:24:45 dillon Exp $
40 * This module implements userland mutex helper functions. umtx_sleep()
41 * handling blocking and umtx_wakeup() handles wakeups. The sleep/wakeup
42 * functions operate on user addresses.
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/kernel.h>
48 #include <sys/sysproto.h>
49 #include <sys/sysunion.h>
50 #include <sys/sysent.h>
51 #include <sys/syscall.h>
52 #include <sys/module.h>
54 #include <cpu/lwbuf.h>
57 #include <vm/vm_param.h>
60 #include <vm/vm_map.h>
61 #include <vm/vm_object.h>
62 #include <vm/vm_page.h>
63 #include <vm/vm_pager.h>
64 #include <vm/vm_pageout.h>
65 #include <vm/vm_extern.h>
66 #include <vm/vm_page.h>
67 #include <vm/vm_kern.h>
69 #include <vm/vm_page2.h>
71 static void umtx_sleep_page_action_cow(vm_page_t m, vm_page_action_t action);
74 * If the contents of the userland-supplied pointer matches the specified
75 * value enter an interruptable sleep for up to <timeout> microseconds.
76 * If the contents does not match then return immediately.
78 * Returns 0 if we slept and were woken up, -1 and EWOULDBLOCK if we slept
79 * and timed out, and EBUSY if the contents of the pointer already does
80 * not match the specified value. A timeout of 0 indicates an unlimited sleep.
81 * EINTR is returned if the call was interrupted by a signal (even if
82 * the signal specifies that the system call should restart).
84 * This function interlocks against call to umtx_wakeup. It does NOT interlock
85 * against changes in *ptr. However, it does not have to. The standard use
86 * of *ptr is to differentiate between an uncontested and a contested mutex
87 * and call umtx_wakeup when releasing a contested mutex. Therefore we can
88 * safely race against changes in *ptr as long as we are properly interlocked
89 * against the umtx_wakeup() call.
91 * The VM page associated with the mutex is held in an attempt to keep
92 * the mutex's physical address consistent, allowing umtx_sleep() and
93 * umtx_wakeup() to use the physical address as their rendezvous. BUT
94 * situations can arise where the physical address may change, particularly
95 * if a threaded program fork()'s and the mutex's memory becomes
96 * copy-on-write. We register an event on the VM page to catch COWs.
98 * umtx_sleep { const int *ptr, int value, int timeout }
101 sys_umtx_sleep(struct umtx_sleep_args *uap)
103 struct lwbuf lwb_cache;
105 struct vm_page_action action;
112 if (uap->timeout < 0)
114 if ((vm_offset_t)uap->ptr & (sizeof(int) - 1))
118 * When faulting in the page, force any COW pages to be resolved.
119 * Otherwise the physical page we sleep on my not match the page
122 lwkt_gettoken(&vm_token);
123 m = vm_fault_page_quick((vm_offset_t)uap->ptr,
124 VM_PROT_READ|VM_PROT_WRITE, &error);
129 lwb = lwbuf_alloc(m, &lwb_cache);
130 offset = (vm_offset_t)uap->ptr & PAGE_MASK;
133 * The critical section is required to interlock the tsleep against
134 * a wakeup from another cpu. The lfence forces synchronization.
136 if (*(int *)(lwbuf_kva(lwb) + offset) == uap->value) {
137 if ((timeout = uap->timeout) != 0) {
138 timeout = (timeout / 1000000) * hz +
139 ((timeout % 1000000) * hz + 999999) / 1000000;
141 waddr = (void *)((intptr_t)VM_PAGE_TO_PHYS(m) + offset);
143 tsleep_interlock(waddr, PCATCH | PDOMAIN_UMTX);
144 if (*(int *)(lwbuf_kva(lwb) + offset) == uap->value) {
145 vm_page_init_action(m, &action, umtx_sleep_page_action_cow, waddr);
146 vm_page_register_action(&action, VMEVENT_COW);
147 if (*(int *)(lwbuf_kva(lwb) + offset) == uap->value) {
148 error = tsleep(waddr, PCATCH | PINTERLOCKED | PDOMAIN_UMTX,
153 vm_page_unregister_action(&action);
158 /* Always break out in case of signal, even if restartable */
159 if (error == ERESTART)
166 /*vm_page_dirty(m); we don't actually dirty the page */
169 lwkt_reltoken(&vm_token);
174 * If this page is being copied it may no longer represent the page
175 * underlying our virtual address. Wake up any umtx_sleep()'s
176 * that were waiting on its physical address to force them to retry.
179 umtx_sleep_page_action_cow(vm_page_t m, vm_page_action_t action)
181 lwkt_gettoken(&vm_token);
182 wakeup_domain(action->data, PDOMAIN_UMTX);
183 lwkt_reltoken(&vm_token);
187 * umtx_wakeup { const int *ptr, int count }
189 * Wakeup the specified number of processes held in umtx_sleep() on the
190 * specified user address. A count of 0 wakes up all waiting processes.
192 * XXX assumes that the physical address space does not exceed the virtual
196 sys_umtx_wakeup(struct umtx_wakeup_args *uap)
204 if ((vm_offset_t)uap->ptr & (sizeof(int) - 1))
206 lwkt_gettoken(&vm_token);
207 m = vm_fault_page_quick((vm_offset_t)uap->ptr, VM_PROT_READ, &error);
212 offset = (vm_offset_t)uap->ptr & PAGE_MASK;
213 waddr = (void *)((intptr_t)VM_PAGE_TO_PHYS(m) + offset);
215 if (uap->count == 1) {
216 wakeup_domain_one(waddr, PDOMAIN_UMTX);
218 /* XXX wakes them all up for now */
219 wakeup_domain(waddr, PDOMAIN_UMTX);
224 lwkt_reltoken(&vm_token);