2 * Copyright (c) 2003,2004,2010,2017 The DragonFly Project.
5 * This code is derived from software contributed to The DragonFly Project
6 * by Matthew Dillon <dillon@backplane.com> and David Xu <davidxu@freebsd.org>
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
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13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
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37 * This module implements userland mutex helper functions. umtx_sleep()
38 * handling blocking and umtx_wakeup() handles wakeups. The sleep/wakeup
39 * functions operate on user addresses.
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/cdefs.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/sysctl.h>
51 #include <sys/module.h>
52 #include <sys/thread.h>
55 #include <cpu/lwbuf.h>
58 #include <vm/vm_param.h>
61 #include <vm/vm_map.h>
62 #include <vm/vm_object.h>
63 #include <vm/vm_page.h>
64 #include <vm/vm_pager.h>
65 #include <vm/vm_pageout.h>
66 #include <vm/vm_extern.h>
67 #include <vm/vm_kern.h>
69 #include <vm/vm_page2.h>
71 #include <machine/vmm.h>
74 * Improve umtx performance by polling for 4000nS before going to sleep.
75 * This can avoid many IPIs in typical pthreads mutex situations.
77 #ifdef _RDTSC_SUPPORTED_
78 static int umtx_delay = 4000; /* nS */
79 SYSCTL_INT(_kern, OID_AUTO, umtx_delay, CTLFLAG_RW,
82 static int umtx_timeout_max = 2000000; /* microseconds */
83 SYSCTL_INT(_kern, OID_AUTO, umtx_timeout_max, CTLFLAG_RW,
84 &umtx_timeout_max, 0, "");
87 * If the contents of the userland-supplied pointer matches the specified
88 * value enter an interruptable sleep for up to <timeout> microseconds.
89 * If the contents does not match then return immediately.
91 * Returns 0 if we slept and were woken up, -1 and EWOULDBLOCK if we slept
92 * and timed out, and EBUSY if the contents of the pointer already does
93 * not match the specified value. A timeout of 0 indicates an unlimited sleep.
94 * EINTR is returned if the call was interrupted by a signal (even if
95 * the signal specifies that the system call should restart).
97 * This function interlocks against call to umtx_wakeup. It does NOT interlock
98 * against changes in *ptr. However, it does not have to. The standard use
99 * of *ptr is to differentiate between an uncontested and a contested mutex
100 * and call umtx_wakeup when releasing a contested mutex. Therefore we can
101 * safely race against changes in *ptr as long as we are properly interlocked
102 * against the umtx_wakeup() call.
104 * For performance reasons, we do not try to track the underlying page for
105 * mapping changes. Instead, the timeout is capped at kern.umtx_timeout_max
106 * (default 1 second) and the caller is expected to retry. The kernel
107 * will wake all umtx_sleep()s if the process fork()s, but not if it vfork()s.
108 * Other mapping changes must be caught by the timeout.
110 * umtx_sleep { const int *ptr, int value, int timeout }
113 sys_umtx_sleep(struct umtx_sleep_args *uap)
124 if (uap->timeout < 0)
130 vmm_vm_get_gpa(td->td_proc, &gpa, (register_t)uap->ptr);
131 uap->ptr = (const int *)gpa;
134 uptr = __DEQUALIFY(void *, uap->ptr);
135 if ((vm_offset_t)uptr & (sizeof(int) - 1))
138 offset = (vm_offset_t)uptr & PAGE_MASK;
141 * Resolve the physical address. We allow the case where there are
142 * sometimes discontinuities (causing a 2 second retry timeout).
144 retry_on_discontinuity:
145 fail_counter = 10000;
147 if (--fail_counter == 0) {
148 kprintf("umtx_sleep() (X): ERROR Discontinuity %p (%s %d/%d)\n",
150 (int)td->td_proc->p_pid,
151 (int)td->td_lwp->lwp_tid);
154 value = fuwordadd32(uptr, 0);
155 waddr = (void *)(intptr_t)uservtophys((intptr_t)uptr);
156 } while (waddr == (void *)(intptr_t)-1 && value != -1);
158 if (value == -1 && waddr == (void *)(intptr_t)-1) {
159 kprintf("umtx_sleep() (A): WARNING can't translate %p (%s %d/%d)\n",
161 (int)td->td_proc->p_pid,
162 (int)td->td_lwp->lwp_tid);
167 if (value == uap->value) {
168 #ifdef _RDTSC_SUPPORTED_
170 * Poll a little while before sleeping, most mutexes are
177 tsc_target = tsc_get_target(umtx_delay);
178 while (tsc_test_target(tsc_target) == 0) {
180 if (fuwordadd32(uptr, 0) != uap->value) {
193 * Calculate the timeout. This will be acccurate to within ~2 ticks.
194 * uap->timeout is in microseconds.
196 timeout = umtx_timeout_max;
197 if (uap->timeout && uap->timeout < timeout)
198 timeout = uap->timeout;
199 timeout = (timeout / 1000000) * hz +
200 ((timeout % 1000000) * hz + 999999) / 1000000;
203 * Wake us up if the memory location COWs while we are sleeping.
204 * Use a critical section to tighten up the interlock. Also,
205 * tsleep_remove() requires the caller be in a critical section.
210 * We must interlock just before sleeping. If we interlock before
211 * registration the lock operations done by the registration can
214 * We cannot leave our interlock hanging on return because this
215 * will interfere with umtx_wakeup() calls with limited wakeup
218 tsleep_interlock(waddr, PCATCH | PDOMAIN_UMTX);
221 * Check physical address changed
224 if ((void *)(intptr_t)uservtophys((intptr_t)uptr) != waddr) {
226 goto retry_on_discontinuity;
232 value = fuwordadd32(uptr, 0);
234 if (value == uap->value) {
235 error = tsleep(waddr, PCATCH | PINTERLOCKED | PDOMAIN_UMTX,
241 /* Always break out in case of signal, even if restartable */
242 if (error == ERESTART)
252 * umtx_wakeup { const int *ptr, int count }
254 * Wakeup the specified number of processes held in umtx_sleep() on the
255 * specified user address. A count of 0 wakes up all waiting processes.
258 sys_umtx_wakeup(struct umtx_wakeup_args *uap)
272 vmm_vm_get_gpa(td->td_proc, &gpa, (register_t)uap->ptr);
273 uap->ptr = (const int *)gpa;
277 * WARNING! We can only use vm_fault_page*() for reading data. We
278 * cannot use it for writing data because there is no pmap
279 * interlock to protect against flushes/pageouts.
282 if ((vm_offset_t)uap->ptr & (sizeof(int) - 1))
285 offset = (vm_offset_t)uap->ptr & PAGE_MASK;
286 uptr = __DEQUALIFY(void *, uap->ptr);
288 fail_counter = 10000;
290 if (--fail_counter == 0) {
291 kprintf("umtx_wakeup() (X): ERROR Discontinuity "
294 (int)td->td_proc->p_pid,
295 (int)td->td_lwp->lwp_tid);
298 value = fuwordadd32(uptr, 0);
299 waddr = (void *)(intptr_t)uservtophys((intptr_t)uptr);
300 } while (waddr == (void *)(intptr_t)-1 && value != -1);
302 if (value == -1 && waddr == (void *)(intptr_t)-1) {
303 kprintf("umtx_wakeup() (A): WARNING can't translate %p (%s %d/%d)\n",
305 (int)td->td_proc->p_pid,
306 (int)td->td_lwp->lwp_tid);
310 if (uap->count == 1) {
311 wakeup_domain_one(waddr, PDOMAIN_UMTX);
313 /* XXX wakes them all up for now */
314 wakeup_domain(waddr, PDOMAIN_UMTX);