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>
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9 * modification, are permitted provided that the following conditions
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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>
53 #include <cpu/lwbuf.h>
56 #include <vm/vm_param.h>
59 #include <vm/vm_map.h>
60 #include <vm/vm_object.h>
61 #include <vm/vm_page.h>
62 #include <vm/vm_pager.h>
63 #include <vm/vm_pageout.h>
64 #include <vm/vm_extern.h>
65 #include <vm/vm_kern.h>
67 #include <vm/vm_page2.h>
69 #include <machine/vmm.h>
72 * Improve umtx performance by polling for 4000nS before going to sleep.
73 * This can avoid many IPIs in typical pthreads mutex situations.
75 #ifdef _RDTSC_SUPPORTED_
76 static int umtx_delay = 4000; /* nS */
77 SYSCTL_INT(_kern, OID_AUTO, umtx_delay, CTLFLAG_RW,
80 static int umtx_timeout_max = 2000000; /* microseconds */
81 SYSCTL_INT(_kern, OID_AUTO, umtx_timeout_max, CTLFLAG_RW,
82 &umtx_timeout_max, 0, "");
85 * If the contents of the userland-supplied pointer matches the specified
86 * value enter an interruptable sleep for up to <timeout> microseconds.
87 * If the contents does not match then return immediately.
89 * Returns 0 if we slept and were woken up, -1 and EWOULDBLOCK if we slept
90 * and timed out, and EBUSY if the contents of the pointer already does
91 * not match the specified value. A timeout of 0 indicates an unlimited sleep.
92 * EINTR is returned if the call was interrupted by a signal (even if
93 * the signal specifies that the system call should restart).
95 * This function interlocks against call to umtx_wakeup. It does NOT interlock
96 * against changes in *ptr. However, it does not have to. The standard use
97 * of *ptr is to differentiate between an uncontested and a contested mutex
98 * and call umtx_wakeup when releasing a contested mutex. Therefore we can
99 * safely race against changes in *ptr as long as we are properly interlocked
100 * against the umtx_wakeup() call.
102 * For performance reasons, we do not try to track the underlying page for
103 * mapping changes. Instead, the timeout is capped at kern.umtx_timeout_max
104 * (default 1 second) and the caller is expected to retry. The kernel
105 * will wake all umtx_sleep()s if the process fork()s, but not if it vfork()s.
106 * Other mapping changes must be caught by the timeout.
108 * umtx_sleep { const int *ptr, int value, int timeout }
111 sys_umtx_sleep(struct umtx_sleep_args *uap)
120 if (uap->timeout < 0)
123 if (curthread->td_vmm) {
125 vmm_vm_get_gpa(curproc, &gpa, (register_t)uap->ptr);
126 uap->ptr = (const int *)gpa;
129 uptr = __DEQUALIFY(void *, uap->ptr);
130 if ((vm_offset_t)uptr & (sizeof(int) - 1))
133 offset = (vm_offset_t)uptr & PAGE_MASK;
136 * Initial quick check. If -1 is returned distinguish between
139 value = fuword32(uptr);
140 if (value == -1 && uservtophys((intptr_t)uap->ptr) == (vm_paddr_t)-1)
144 if (value == uap->value) {
145 #ifdef _RDTSC_SUPPORTED_
147 * Poll a little while before sleeping, most mutexes are
154 tsc_target = tsc_get_target(umtx_delay);
155 while (tsc_test_target(tsc_target) == 0) {
157 if (fuword32(uptr) != uap->value) {
170 * Calculate the timeout. This will be acccurate to within ~2 ticks.
171 * uap->timeout is in microseconds.
173 timeout = umtx_timeout_max;
174 if (uap->timeout && uap->timeout < timeout)
175 timeout = uap->timeout;
176 timeout = (timeout / 1000000) * hz +
177 ((timeout % 1000000) * hz + 999999) / 1000000;
180 * Calculate the physical address of the mutex. This gives us
181 * good distribution between unrelated processes using the
184 waddr = (void *)uservtophys((intptr_t)uap->ptr);
185 if (waddr == (void *)(intptr_t)-1) {
191 * Wake us up if the memory location COWs while we are sleeping.
192 * Use a critical section to tighten up the interlock. Also,
193 * tsleep_remove() requires the caller be in a critical section.
198 * We must interlock just before sleeping. If we interlock before
199 * registration the lock operations done by the registration can
202 * We cannot leave our interlock hanging on return because this
203 * will interfere with umtx_wakeup() calls with limited wakeup
206 tsleep_interlock(waddr, PCATCH | PDOMAIN_UMTX);
208 if (fuword32(uptr) == uap->value) {
209 error = tsleep(waddr, PCATCH | PINTERLOCKED | PDOMAIN_UMTX,
215 /* Always break out in case of signal, even if restartable */
216 if (error == ERESTART)
226 * umtx_wakeup { const int *ptr, int count }
228 * Wakeup the specified number of processes held in umtx_sleep() on the
229 * specified user address. A count of 0 wakes up all waiting processes.
232 sys_umtx_wakeup(struct umtx_wakeup_args *uap)
238 if (curthread->td_vmm) {
240 vmm_vm_get_gpa(curproc, &gpa, (register_t)uap->ptr);
241 uap->ptr = (const int *)gpa;
245 * WARNING! We can only use vm_fault_page*() for reading data. We
246 * cannot use it for writing data because there is no pmap
247 * interlock to protect against flushes/pageouts.
250 if ((vm_offset_t)uap->ptr & (sizeof(int) - 1))
253 offset = (vm_offset_t)uap->ptr & PAGE_MASK;
254 waddr = (void *)uservtophys((intptr_t)uap->ptr);
255 if (waddr == (void *)(intptr_t)-1)
258 if (uap->count == 1) {
259 wakeup_domain_one(waddr, PDOMAIN_UMTX);
261 /* XXX wakes them all up for now */
262 wakeup_domain(waddr, PDOMAIN_UMTX);