coroutine-ucontext.c

   1 /*
   2  * ucontext coroutine initialization code
   3  *
   4  * Copyright (C) 2006  Anthony Liguori <anthony@codemonkey.ws>
   5  * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.0 of the License, or (at your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 /* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
  22 #ifdef _FORTIFY_SOURCE
  23 #undef _FORTIFY_SOURCE
  24 #endif
  25 #include <stdlib.h>
  26 #include <setjmp.h>
  27 #include <stdint.h>
  28 #include <pthread.h>
  29 #include <ucontext.h>
  30 #include "qemu-common.h"
  31 #include "qemu-coroutine-int.h"
  32
  33 #ifdef CONFIG_VALGRIND_H
  34 #include <valgrind/valgrind.h>
  35 #endif
  36
  37 enum {
  38     /* Maximum free pool size prevents holding too many freed coroutines */
  39     POOL_MAX_SIZE = 64,
  40 };
  41
  42 /** Free list to speed up creation */
  43 static QSLIST_HEAD(, Coroutine) pool = QSLIST_HEAD_INITIALIZER(pool);
  44 static unsigned int pool_size;
  45
  46 typedef struct {
  47     Coroutine base;
  48     void *stack;
  49     jmp_buf env;
  50
  51 #ifdef CONFIG_VALGRIND_H
  52     unsigned int valgrind_stack_id;
  53 #endif
  54
  55 } CoroutineUContext;
  56
  57 /**
  58  * Per-thread coroutine bookkeeping
  59  */
  60 typedef struct {
  61     /** Currently executing coroutine */
  62     Coroutine *current;
  63
  64     /** The default coroutine */
  65     CoroutineUContext leader;
  66 } CoroutineThreadState;
  67
  68 static pthread_key_t thread_state_key;
  69
  70 /*
  71  * va_args to makecontext() must be type 'int', so passing
  72  * the pointer we need may require several int args. This
  73  * union is a quick hack to let us do that
  74  */
  75 union cc_arg {
  76     void *p;
  77     int i[2];
  78 };
  79
  80 static CoroutineThreadState *coroutine_get_thread_state(void)
  81 {
  82     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
  83
  84     if (!s) {
  85         s = g_malloc0(sizeof(*s));
  86         s->current = &s->leader.base;
  87         pthread_setspecific(thread_state_key, s);
  88     }
  89     return s;
  90 }
  91
  92 static void qemu_coroutine_thread_cleanup(void *opaque)
  93 {
  94     CoroutineThreadState *s = opaque;
  95
  96     g_free(s);
  97 }
  98
  99 static void __attribute__((destructor)) coroutine_cleanup(void)
 100 {
 101     Coroutine *co;
 102     Coroutine *tmp;
 103
 104     QSLIST_FOREACH_SAFE(co, &pool, pool_next, tmp) {
 105         g_free(DO_UPCAST(CoroutineUContext, base, co)->stack);
 106         g_free(co);
 107     }
 108 }
 109
 110 static void __attribute__((constructor)) coroutine_init(void)
 111 {
 112     int ret;
 113
 114     ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
 115     if (ret != 0) {
 116         fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
 117         abort();
 118     }
 119 }
 120
 121 static void coroutine_trampoline(int i0, int i1)
 122 {
 123     union cc_arg arg;
 124     CoroutineUContext *self;
 125     Coroutine *co;
 126
 127     arg.i[0] = i0;
 128     arg.i[1] = i1;
 129     self = arg.p;
 130     co = &self->base;
 131
 132     /* Initialize longjmp environment and switch back the caller */
 133     if (!setjmp(self->env)) {
 134         longjmp(*(jmp_buf *)co->entry_arg, 1);
 135     }
 136
 137     while (true) {
 138         co->entry(co->entry_arg);
 139         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 140     }
 141 }
 142
 143 static Coroutine *coroutine_new(void)
 144 {
 145     const size_t stack_size = 1 << 20;
 146     CoroutineUContext *co;
 147     ucontext_t old_uc, uc;
 148     jmp_buf old_env;
 149     union cc_arg arg = {0};
 150
 151     /* The ucontext functions preserve signal masks which incurs a system call
 152      * overhead.  setjmp()/longjmp() does not preserve signal masks but only
 153      * works on the current stack.  Since we need a way to create and switch to
 154      * a new stack, use the ucontext functions for that but setjmp()/longjmp()
 155      * for everything else.
 156      */
 157
 158     if (getcontext(&uc) == -1) {
 159         abort();
 160     }
 161
 162     co = g_malloc0(sizeof(*co));
 163     co->stack = g_malloc(stack_size);
 164     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 165
 166     uc.uc_link = &old_uc;
 167     uc.uc_stack.ss_sp = co->stack;
 168     uc.uc_stack.ss_size = stack_size;
 169     uc.uc_stack.ss_flags = 0;
 170
 171 #ifdef CONFIG_VALGRIND_H
 172     co->valgrind_stack_id =
 173         VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size);
 174 #endif
 175
 176     arg.p = co;
 177
 178     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 179                 2, arg.i[0], arg.i[1]);
 180
 181     /* swapcontext() in, longjmp() back out */
 182     if (!setjmp(old_env)) {
 183         swapcontext(&old_uc, &uc);
 184     }
 185     return &co->base;
 186 }
 187
 188 Coroutine *qemu_coroutine_new(void)
 189 {
 190     Coroutine *co;
 191
 192     co = QSLIST_FIRST(&pool);
 193     if (co) {
 194         QSLIST_REMOVE_HEAD(&pool, pool_next);
 195         pool_size--;
 196     } else {
 197         co = coroutine_new();
 198     }
 199     return co;
 200 }
 201
 202 #ifdef CONFIG_VALGRIND_H
 203 /* Work around an unused variable in the valgrind.h macro... */
 204 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 205 static inline void valgrind_stack_deregister(CoroutineUContext *co)
 206 {
 207     VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
 208 }
 209 #pragma GCC diagnostic error "-Wunused-but-set-variable"
 210 #endif
 211
 212 void qemu_coroutine_delete(Coroutine *co_)
 213 {
 214     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 215
 216     if (pool_size < POOL_MAX_SIZE) {
 217         QSLIST_INSERT_HEAD(&pool, &co->base, pool_next);
 218         co->base.caller = NULL;
 219         pool_size++;
 220         return;
 221     }
 222
 223 #ifdef CONFIG_VALGRIND_H
 224     valgrind_stack_deregister(co);
 225 #endif
 226
 227     g_free(co->stack);
 228     g_free(co);
 229 }
 230
 231 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 232                                       CoroutineAction action)
 233 {
 234     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 235     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 236     CoroutineThreadState *s = coroutine_get_thread_state();
 237     int ret;
 238
 239     s->current = to_;
 240
 241     ret = setjmp(from->env);
 242     if (ret == 0) {
 243         longjmp(to->env, action);
 244     }
 245     return ret;
 246 }
 247
 248 Coroutine *qemu_coroutine_self(void)
 249 {
 250     CoroutineThreadState *s = coroutine_get_thread_state();
 251
 252     return s->current;
 253 }
 254
 255 bool qemu_in_coroutine(void)
 256 {
 257     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
 258
 259     return s && s->current->caller;
 260 }