1 /* 2 * fs/timerfd.c 3 * 4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> 5 * 6 * 7 * Thanks to Thomas Gleixner for code reviews and useful comments. 8 * 9 */ 10 11 #include <linux/file.h> 12 #include <linux/poll.h> 13 #include <linux/init.h> 14 #include <linux/fs.h> 15 #include <linux/sched.h> 16 #include <linux/kernel.h> 17 #include <linux/slab.h> 18 #include <linux/list.h> 19 #include <linux/spinlock.h> 20 #include <linux/time.h> 21 #include <linux/hrtimer.h> 22 #include <linux/anon_inodes.h> 23 #include <linux/timerfd.h> 24 #include <linux/syscalls.h> 25 #include <linux/rcupdate.h> 26 27 struct timerfd_ctx { 28 struct hrtimer tmr; 29 ktime_t tintv; 30 ktime_t moffs; 31 wait_queue_head_t wqh; 32 u64 ticks; 33 int expired; 34 int clockid; 35 struct rcu_head rcu; 36 struct list_head clist; 37 bool might_cancel; 38 }; 39 40 static LIST_HEAD(cancel_list); 41 static DEFINE_SPINLOCK(cancel_lock); 42 43 /* 44 * This gets called when the timer event triggers. We set the "expired" 45 * flag, but we do not re-arm the timer (in case it's necessary, 46 * tintv.tv64 != 0) until the timer is accessed. 47 */ 48 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) 49 { 50 struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); 51 unsigned long flags; 52 53 spin_lock_irqsave(&ctx->wqh.lock, flags); 54 ctx->expired = 1; 55 ctx->ticks++; 56 wake_up_locked(&ctx->wqh); 57 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 58 59 return HRTIMER_NORESTART; 60 } 61 62 /* 63 * Called when the clock was set to cancel the timers in the cancel 64 * list. This will wake up processes waiting on these timers. The 65 * wake-up requires ctx->ticks to be non zero, therefore we increment 66 * it before calling wake_up_locked(). 67 */ 68 void timerfd_clock_was_set(void) 69 { 70 ktime_t moffs = ktime_get_monotonic_offset(); 71 struct timerfd_ctx *ctx; 72 unsigned long flags; 73 74 rcu_read_lock(); 75 list_for_each_entry_rcu(ctx, &cancel_list, clist) { 76 if (!ctx->might_cancel) 77 continue; 78 spin_lock_irqsave(&ctx->wqh.lock, flags); 79 if (ctx->moffs.tv64 != moffs.tv64) { 80 ctx->moffs.tv64 = KTIME_MAX; 81 ctx->ticks++; 82 wake_up_locked(&ctx->wqh); 83 } 84 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 85 } 86 rcu_read_unlock(); 87 } 88 89 static void timerfd_remove_cancel(struct timerfd_ctx *ctx) 90 { 91 if (ctx->might_cancel) { 92 ctx->might_cancel = false; 93 spin_lock(&cancel_lock); 94 list_del_rcu(&ctx->clist); 95 spin_unlock(&cancel_lock); 96 } 97 } 98 99 static bool timerfd_canceled(struct timerfd_ctx *ctx) 100 { 101 if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX) 102 return false; 103 ctx->moffs = ktime_get_monotonic_offset(); 104 return true; 105 } 106 107 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags) 108 { 109 if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) && 110 (flags & TFD_TIMER_CANCEL_ON_SET)) { 111 if (!ctx->might_cancel) { 112 ctx->might_cancel = true; 113 spin_lock(&cancel_lock); 114 list_add_rcu(&ctx->clist, &cancel_list); 115 spin_unlock(&cancel_lock); 116 } 117 } else if (ctx->might_cancel) { 118 timerfd_remove_cancel(ctx); 119 } 120 } 121 122 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) 123 { 124 ktime_t remaining; 125 126 remaining = hrtimer_expires_remaining(&ctx->tmr); 127 return remaining.tv64 < 0 ? ktime_set(0, 0): remaining; 128 } 129 130 static int timerfd_setup(struct timerfd_ctx *ctx, int flags, 131 const struct itimerspec *ktmr) 132 { 133 enum hrtimer_mode htmode; 134 ktime_t texp; 135 int clockid = ctx->clockid; 136 137 htmode = (flags & TFD_TIMER_ABSTIME) ? 138 HRTIMER_MODE_ABS: HRTIMER_MODE_REL; 139 140 texp = timespec_to_ktime(ktmr->it_value); 141 ctx->expired = 0; 142 ctx->ticks = 0; 143 ctx->tintv = timespec_to_ktime(ktmr->it_interval); 144 hrtimer_init(&ctx->tmr, clockid, htmode); 145 hrtimer_set_expires(&ctx->tmr, texp); 146 ctx->tmr.function = timerfd_tmrproc; 147 if (texp.tv64 != 0) { 148 hrtimer_start(&ctx->tmr, texp, htmode); 149 if (timerfd_canceled(ctx)) 150 return -ECANCELED; 151 } 152 return 0; 153 } 154 155 static int timerfd_release(struct inode *inode, struct file *file) 156 { 157 struct timerfd_ctx *ctx = file->private_data; 158 159 timerfd_remove_cancel(ctx); 160 hrtimer_cancel(&ctx->tmr); 161 kfree_rcu(ctx, rcu); 162 return 0; 163 } 164 165 static unsigned int timerfd_poll(struct file *file, poll_table *wait) 166 { 167 struct timerfd_ctx *ctx = file->private_data; 168 unsigned int events = 0; 169 unsigned long flags; 170 171 poll_wait(file, &ctx->wqh, wait); 172 173 spin_lock_irqsave(&ctx->wqh.lock, flags); 174 if (ctx->ticks) 175 events |= POLLIN; 176 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 177 178 return events; 179 } 180 181 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, 182 loff_t *ppos) 183 { 184 struct timerfd_ctx *ctx = file->private_data; 185 ssize_t res; 186 u64 ticks = 0; 187 188 if (count < sizeof(ticks)) 189 return -EINVAL; 190 spin_lock_irq(&ctx->wqh.lock); 191 if (file->f_flags & O_NONBLOCK) 192 res = -EAGAIN; 193 else 194 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks); 195 196 /* 197 * If clock has changed, we do not care about the 198 * ticks and we do not rearm the timer. Userspace must 199 * reevaluate anyway. 200 */ 201 if (timerfd_canceled(ctx)) { 202 ctx->ticks = 0; 203 ctx->expired = 0; 204 res = -ECANCELED; 205 } 206 207 if (ctx->ticks) { 208 ticks = ctx->ticks; 209 210 if (ctx->expired && ctx->tintv.tv64) { 211 /* 212 * If tintv.tv64 != 0, this is a periodic timer that 213 * needs to be re-armed. We avoid doing it in the timer 214 * callback to avoid DoS attacks specifying a very 215 * short timer period. 216 */ 217 ticks += hrtimer_forward_now(&ctx->tmr, 218 ctx->tintv) - 1; 219 hrtimer_restart(&ctx->tmr); 220 } 221 ctx->expired = 0; 222 ctx->ticks = 0; 223 } 224 spin_unlock_irq(&ctx->wqh.lock); 225 if (ticks) 226 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks); 227 return res; 228 } 229 230 static const struct file_operations timerfd_fops = { 231 .release = timerfd_release, 232 .poll = timerfd_poll, 233 .read = timerfd_read, 234 .llseek = noop_llseek, 235 }; 236 237 static struct file *timerfd_fget(int fd) 238 { 239 struct file *file; 240 241 file = fget(fd); 242 if (!file) 243 return ERR_PTR(-EBADF); 244 if (file->f_op != &timerfd_fops) { 245 fput(file); 246 return ERR_PTR(-EINVAL); 247 } 248 249 return file; 250 } 251 252 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags) 253 { 254 int ufd; 255 struct timerfd_ctx *ctx; 256 257 /* Check the TFD_* constants for consistency. */ 258 BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC); 259 BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK); 260 261 if ((flags & ~TFD_CREATE_FLAGS) || 262 (clockid != CLOCK_MONOTONIC && 263 clockid != CLOCK_REALTIME)) 264 return -EINVAL; 265 266 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 267 if (!ctx) 268 return -ENOMEM; 269 270 init_waitqueue_head(&ctx->wqh); 271 ctx->clockid = clockid; 272 hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS); 273 ctx->moffs = ktime_get_monotonic_offset(); 274 275 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx, 276 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS)); 277 if (ufd < 0) 278 kfree(ctx); 279 280 return ufd; 281 } 282 283 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags, 284 const struct itimerspec __user *, utmr, 285 struct itimerspec __user *, otmr) 286 { 287 struct file *file; 288 struct timerfd_ctx *ctx; 289 struct itimerspec ktmr, kotmr; 290 int ret; 291 292 if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) 293 return -EFAULT; 294 295 if ((flags & ~TFD_SETTIME_FLAGS) || 296 !timespec_valid(&ktmr.it_value) || 297 !timespec_valid(&ktmr.it_interval)) 298 return -EINVAL; 299 300 file = timerfd_fget(ufd); 301 if (IS_ERR(file)) 302 return PTR_ERR(file); 303 ctx = file->private_data; 304 305 timerfd_setup_cancel(ctx, flags); 306 307 /* 308 * We need to stop the existing timer before reprogramming 309 * it to the new values. 310 */ 311 for (;;) { 312 spin_lock_irq(&ctx->wqh.lock); 313 if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) 314 break; 315 spin_unlock_irq(&ctx->wqh.lock); 316 cpu_relax(); 317 } 318 319 /* 320 * If the timer is expired and it's periodic, we need to advance it 321 * because the caller may want to know the previous expiration time. 322 * We do not update "ticks" and "expired" since the timer will be 323 * re-programmed again in the following timerfd_setup() call. 324 */ 325 if (ctx->expired && ctx->tintv.tv64) 326 hrtimer_forward_now(&ctx->tmr, ctx->tintv); 327 328 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 329 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 330 331 /* 332 * Re-program the timer to the new value ... 333 */ 334 ret = timerfd_setup(ctx, flags, &ktmr); 335 336 spin_unlock_irq(&ctx->wqh.lock); 337 fput(file); 338 if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr))) 339 return -EFAULT; 340 341 return ret; 342 } 343 344 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr) 345 { 346 struct file *file; 347 struct timerfd_ctx *ctx; 348 struct itimerspec kotmr; 349 350 file = timerfd_fget(ufd); 351 if (IS_ERR(file)) 352 return PTR_ERR(file); 353 ctx = file->private_data; 354 355 spin_lock_irq(&ctx->wqh.lock); 356 if (ctx->expired && ctx->tintv.tv64) { 357 ctx->expired = 0; 358 ctx->ticks += 359 hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1; 360 hrtimer_restart(&ctx->tmr); 361 } 362 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 363 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 364 spin_unlock_irq(&ctx->wqh.lock); 365 fput(file); 366 367 return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0; 368 } 369 370