2 * Copyright (c) 2003,2004 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com> and David Xu <davidxu@freebsd.org>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * $DragonFly: src/sys/kern/kern_umtx.c,v 1.9 2008/05/09 07:24:45 dillon Exp $
38 * This module implements userland mutex helper functions. umtx_sleep()
39 * handling blocking and umtx_wakeup() handles wakeups. The sleep/wakeup
40 * functions operate on user addresses.
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/kernel.h>
46 #include <sys/sysproto.h>
47 #include <sys/sysunion.h>
48 #include <sys/sysent.h>
49 #include <sys/syscall.h>
50 #include <sys/sfbuf.h>
51 #include <sys/module.h>
54 #include <vm/vm_param.h>
57 #include <vm/vm_map.h>
58 #include <vm/vm_object.h>
59 #include <vm/vm_page.h>
60 #include <vm/vm_pager.h>
61 #include <vm/vm_pageout.h>
62 #include <vm/vm_extern.h>
63 #include <vm/vm_page.h>
64 #include <vm/vm_kern.h>
66 #include <vm/vm_page2.h>
67 #include <sys/mplock2.h>
69 static void umtx_sleep_page_action_cow(vm_page_t m
, vm_page_action_t action
);
72 * If the contents of the userland-supplied pointer matches the specified
73 * value enter an interruptable sleep for up to <timeout> microseconds.
74 * If the contents does not match then return immediately.
76 * Returns 0 if we slept and were woken up, -1 and EWOULDBLOCK if we slept
77 * and timed out, and EBUSY if the contents of the pointer already does
78 * not match the specified value. A timeout of 0 indicates an unlimited sleep.
79 * EINTR is returned if the call was interrupted by a signal (even if
80 * the signal specifies that the system call should restart).
82 * This function interlocks against call to umtx_wakeup. It does NOT interlock
83 * against changes in *ptr. However, it does not have to. The standard use
84 * of *ptr is to differentiate between an uncontested and a contested mutex
85 * and call umtx_wakeup when releasing a contested mutex. Therefore we can
86 * safely race against changes in *ptr as long as we are properly interlocked
87 * against the umtx_wakeup() call.
89 * The VM page associated with the mutex is held in an attempt to keep
90 * the mutex's physical address consistent, allowing umtx_sleep() and
91 * umtx_wakeup() to use the physical address as their rendezvous. BUT
92 * situations can arise where the physical address may change, particularly
93 * if a threaded program fork()'s and the mutex's memory becomes
94 * copy-on-write. We register an event on the VM page to catch COWs.
96 * umtx_sleep { const int *ptr, int value, int timeout }
101 sys_umtx_sleep(struct umtx_sleep_args
*uap
)
105 struct vm_page_action action
;
111 if (uap
->timeout
< 0)
113 if ((vm_offset_t
)uap
->ptr
& (sizeof(int) - 1))
117 * When faulting in the page, force any COW pages to be resolved.
118 * Otherwise the physical page we sleep on my not match the page
122 m
= vm_fault_page_quick((vm_offset_t
)uap
->ptr
, VM_PROT_READ
|VM_PROT_WRITE
, &error
);
127 sf
= sf_buf_alloc(m
, SFB_CPUPRIVATE
);
128 offset
= (vm_offset_t
)uap
->ptr
& PAGE_MASK
;
131 * The critical section is required to interlock the tsleep against
132 * a wakeup from another cpu. The lfence forces synchronization.
134 if (*(int *)(sf_buf_kva(sf
) + offset
) == uap
->value
) {
135 if ((timeout
= uap
->timeout
) != 0) {
136 timeout
= (timeout
/ 1000000) * hz
+
137 ((timeout
% 1000000) * hz
+ 999999) / 1000000;
139 waddr
= (void *)((intptr_t)VM_PAGE_TO_PHYS(m
) + offset
);
141 tsleep_interlock(waddr
, PCATCH
| PDOMAIN_UMTX
);
142 if (*(int *)(sf_buf_kva(sf
) + offset
) == uap
->value
) {
143 vm_page_init_action(&action
, umtx_sleep_page_action_cow
, waddr
);
144 vm_page_register_action(m
, &action
, VMEVENT_COW
);
145 error
= tsleep(waddr
, PCATCH
| PINTERLOCKED
| PDOMAIN_UMTX
,
147 vm_page_unregister_action(m
, &action
);
152 /* Always break out in case of signal, even if restartable */
153 if (error
== ERESTART
)
160 /*vm_page_dirty(m); we don't actually dirty the page */
168 * If this page is being copied it may no longer represent the page
169 * underlying our virtual address. Wake up any umtx_sleep()'s
170 * that were waiting on its physical address to force them to retry.
173 umtx_sleep_page_action_cow(vm_page_t m
, vm_page_action_t action
)
175 wakeup_domain(action
->data
, PDOMAIN_UMTX
);
179 * umtx_wakeup { const int *ptr, int count }
181 * Wakeup the specified number of processes held in umtx_sleep() on the
182 * specified user address. A count of 0 wakes up all waiting processes.
184 * XXX assumes that the physical address space does not exceed the virtual
190 sys_umtx_wakeup(struct umtx_wakeup_args
*uap
)
198 if ((vm_offset_t
)uap
->ptr
& (sizeof(int) - 1))
201 m
= vm_fault_page_quick((vm_offset_t
)uap
->ptr
, VM_PROT_READ
, &error
);
206 offset
= (vm_offset_t
)uap
->ptr
& PAGE_MASK
;
207 waddr
= (void *)((intptr_t)VM_PAGE_TO_PHYS(m
) + offset
);
209 if (uap
->count
== 1) {
210 wakeup_domain_one(waddr
, PDOMAIN_UMTX
);
212 /* XXX wakes them all up for now */
213 wakeup_domain(waddr
, PDOMAIN_UMTX
);