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/list.h> 18 #include <linux/spinlock.h> 19 #include <linux/time.h> 20 #include <linux/hrtimer.h> 21 #include <linux/anon_inodes.h> 22 #include <linux/timerfd.h> 23 #include <linux/syscalls.h> 24 25 struct timerfd_ctx { 26 struct hrtimer tmr; 27 ktime_t tintv; 28 wait_queue_head_t wqh; 29 u64 ticks; 30 int expired; 31 int clockid; 32 }; 33 34 /* 35 * This gets called when the timer event triggers. We set the "expired" 36 * flag, but we do not re-arm the timer (in case it's necessary, 37 * tintv.tv64 != 0) until the timer is accessed. 38 */ 39 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) 40 { 41 struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); 42 unsigned long flags; 43 44 spin_lock_irqsave(&ctx->wqh.lock, flags); 45 ctx->expired = 1; 46 ctx->ticks++; 47 wake_up_locked(&ctx->wqh); 48 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 49 50 return HRTIMER_NORESTART; 51 } 52 53 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) 54 { 55 ktime_t remaining; 56 57 remaining = hrtimer_expires_remaining(&ctx->tmr); 58 return remaining.tv64 < 0 ? ktime_set(0, 0): remaining; 59 } 60 61 static void timerfd_setup(struct timerfd_ctx *ctx, int flags, 62 const struct itimerspec *ktmr) 63 { 64 enum hrtimer_mode htmode; 65 ktime_t texp; 66 67 htmode = (flags & TFD_TIMER_ABSTIME) ? 68 HRTIMER_MODE_ABS: HRTIMER_MODE_REL; 69 70 texp = timespec_to_ktime(ktmr->it_value); 71 ctx->expired = 0; 72 ctx->ticks = 0; 73 ctx->tintv = timespec_to_ktime(ktmr->it_interval); 74 hrtimer_init(&ctx->tmr, ctx->clockid, htmode); 75 hrtimer_set_expires(&ctx->tmr, texp); 76 ctx->tmr.function = timerfd_tmrproc; 77 if (texp.tv64 != 0) 78 hrtimer_start(&ctx->tmr, texp, htmode); 79 } 80 81 static int timerfd_release(struct inode *inode, struct file *file) 82 { 83 struct timerfd_ctx *ctx = file->private_data; 84 85 hrtimer_cancel(&ctx->tmr); 86 kfree(ctx); 87 return 0; 88 } 89 90 static unsigned int timerfd_poll(struct file *file, poll_table *wait) 91 { 92 struct timerfd_ctx *ctx = file->private_data; 93 unsigned int events = 0; 94 unsigned long flags; 95 96 poll_wait(file, &ctx->wqh, wait); 97 98 spin_lock_irqsave(&ctx->wqh.lock, flags); 99 if (ctx->ticks) 100 events |= POLLIN; 101 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 102 103 return events; 104 } 105 106 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, 107 loff_t *ppos) 108 { 109 struct timerfd_ctx *ctx = file->private_data; 110 ssize_t res; 111 u64 ticks = 0; 112 DECLARE_WAITQUEUE(wait, current); 113 114 if (count < sizeof(ticks)) 115 return -EINVAL; 116 spin_lock_irq(&ctx->wqh.lock); 117 res = -EAGAIN; 118 if (!ctx->ticks && !(file->f_flags & O_NONBLOCK)) { 119 __add_wait_queue(&ctx->wqh, &wait); 120 for (res = 0;;) { 121 set_current_state(TASK_INTERRUPTIBLE); 122 if (ctx->ticks) { 123 res = 0; 124 break; 125 } 126 if (signal_pending(current)) { 127 res = -ERESTARTSYS; 128 break; 129 } 130 spin_unlock_irq(&ctx->wqh.lock); 131 schedule(); 132 spin_lock_irq(&ctx->wqh.lock); 133 } 134 __remove_wait_queue(&ctx->wqh, &wait); 135 __set_current_state(TASK_RUNNING); 136 } 137 if (ctx->ticks) { 138 ticks = ctx->ticks; 139 if (ctx->expired && ctx->tintv.tv64) { 140 /* 141 * If tintv.tv64 != 0, this is a periodic timer that 142 * needs to be re-armed. We avoid doing it in the timer 143 * callback to avoid DoS attacks specifying a very 144 * short timer period. 145 */ 146 ticks += hrtimer_forward_now(&ctx->tmr, 147 ctx->tintv) - 1; 148 hrtimer_restart(&ctx->tmr); 149 } 150 ctx->expired = 0; 151 ctx->ticks = 0; 152 } 153 spin_unlock_irq(&ctx->wqh.lock); 154 if (ticks) 155 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks); 156 return res; 157 } 158 159 static const struct file_operations timerfd_fops = { 160 .release = timerfd_release, 161 .poll = timerfd_poll, 162 .read = timerfd_read, 163 }; 164 165 static struct file *timerfd_fget(int fd) 166 { 167 struct file *file; 168 169 file = fget(fd); 170 if (!file) 171 return ERR_PTR(-EBADF); 172 if (file->f_op != &timerfd_fops) { 173 fput(file); 174 return ERR_PTR(-EINVAL); 175 } 176 177 return file; 178 } 179 180 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags) 181 { 182 int ufd; 183 struct timerfd_ctx *ctx; 184 185 /* Check the TFD_* constants for consistency. */ 186 BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC); 187 BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK); 188 189 if ((flags & ~TFD_CREATE_FLAGS) || 190 (clockid != CLOCK_MONOTONIC && 191 clockid != CLOCK_REALTIME)) 192 return -EINVAL; 193 194 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 195 if (!ctx) 196 return -ENOMEM; 197 198 init_waitqueue_head(&ctx->wqh); 199 ctx->clockid = clockid; 200 hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS); 201 202 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx, 203 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS)); 204 if (ufd < 0) 205 kfree(ctx); 206 207 return ufd; 208 } 209 210 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags, 211 const struct itimerspec __user *, utmr, 212 struct itimerspec __user *, otmr) 213 { 214 struct file *file; 215 struct timerfd_ctx *ctx; 216 struct itimerspec ktmr, kotmr; 217 218 if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) 219 return -EFAULT; 220 221 if ((flags & ~TFD_SETTIME_FLAGS) || 222 !timespec_valid(&ktmr.it_value) || 223 !timespec_valid(&ktmr.it_interval)) 224 return -EINVAL; 225 226 file = timerfd_fget(ufd); 227 if (IS_ERR(file)) 228 return PTR_ERR(file); 229 ctx = file->private_data; 230 231 /* 232 * We need to stop the existing timer before reprogramming 233 * it to the new values. 234 */ 235 for (;;) { 236 spin_lock_irq(&ctx->wqh.lock); 237 if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) 238 break; 239 spin_unlock_irq(&ctx->wqh.lock); 240 cpu_relax(); 241 } 242 243 /* 244 * If the timer is expired and it's periodic, we need to advance it 245 * because the caller may want to know the previous expiration time. 246 * We do not update "ticks" and "expired" since the timer will be 247 * re-programmed again in the following timerfd_setup() call. 248 */ 249 if (ctx->expired && ctx->tintv.tv64) 250 hrtimer_forward_now(&ctx->tmr, ctx->tintv); 251 252 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 253 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 254 255 /* 256 * Re-program the timer to the new value ... 257 */ 258 timerfd_setup(ctx, flags, &ktmr); 259 260 spin_unlock_irq(&ctx->wqh.lock); 261 fput(file); 262 if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr))) 263 return -EFAULT; 264 265 return 0; 266 } 267 268 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr) 269 { 270 struct file *file; 271 struct timerfd_ctx *ctx; 272 struct itimerspec kotmr; 273 274 file = timerfd_fget(ufd); 275 if (IS_ERR(file)) 276 return PTR_ERR(file); 277 ctx = file->private_data; 278 279 spin_lock_irq(&ctx->wqh.lock); 280 if (ctx->expired && ctx->tintv.tv64) { 281 ctx->expired = 0; 282 ctx->ticks += 283 hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1; 284 hrtimer_restart(&ctx->tmr); 285 } 286 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 287 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 288 spin_unlock_irq(&ctx->wqh.lock); 289 fput(file); 290 291 return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0; 292 } 293 294