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Davide Libenzifba2afa2007-05-10 22:23:13 -07001/*
2 * fs/signalfd.c
3 *
4 * Copyright (C) 2003 Linus Torvalds
5 *
6 * Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
7 * Changed ->read() to return a siginfo strcture instead of signal number.
8 * Fixed locking in ->poll().
9 * Added sighand-detach notification.
10 * Added fd re-use in sys_signalfd() syscall.
11 * Now using anonymous inode source.
12 * Thanks to Oleg Nesterov for useful code review and suggestions.
13 * More comments and suggestions from Arnd Bergmann.
Davi Arnautb3762bf2007-05-23 13:58:04 -070014 * Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
15 * Retrieve multiple signals with one read() call
Davide Libenzifba2afa2007-05-10 22:23:13 -070016 */
17
18#include <linux/file.h>
19#include <linux/poll.h>
20#include <linux/init.h>
21#include <linux/fs.h>
22#include <linux/sched.h>
23#include <linux/kernel.h>
24#include <linux/signal.h>
25#include <linux/list.h>
26#include <linux/anon_inodes.h>
27#include <linux/signalfd.h>
28
29struct signalfd_ctx {
30 struct list_head lnk;
31 wait_queue_head_t wqh;
32 sigset_t sigmask;
33 struct task_struct *tsk;
34};
35
36struct signalfd_lockctx {
37 struct task_struct *tsk;
38 unsigned long flags;
39};
40
41/*
42 * Tries to acquire the sighand lock. We do not increment the sighand
43 * use count, and we do not even pin the task struct, so we need to
44 * do it inside an RCU read lock, and we must be prepared for the
45 * ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
46 * being detached. We return 0 if the sighand has been detached, or
47 * 1 if we were able to pin the sighand lock.
48 */
49static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
50{
51 struct sighand_struct *sighand = NULL;
52
53 rcu_read_lock();
54 lk->tsk = rcu_dereference(ctx->tsk);
55 if (likely(lk->tsk != NULL))
56 sighand = lock_task_sighand(lk->tsk, &lk->flags);
57 rcu_read_unlock();
58
59 if (sighand && !ctx->tsk) {
60 unlock_task_sighand(lk->tsk, &lk->flags);
61 sighand = NULL;
62 }
63
64 return sighand != NULL;
65}
66
67static void signalfd_unlock(struct signalfd_lockctx *lk)
68{
69 unlock_task_sighand(lk->tsk, &lk->flags);
70}
71
72/*
73 * This must be called with the sighand lock held.
74 */
75void signalfd_deliver(struct task_struct *tsk, int sig)
76{
77 struct sighand_struct *sighand = tsk->sighand;
78 struct signalfd_ctx *ctx, *tmp;
79
80 BUG_ON(!sig);
81 list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
82 /*
83 * We use a negative signal value as a way to broadcast that the
84 * sighand has been orphaned, so that we can notify all the
85 * listeners about this. Remember the ctx->sigmask is inverted,
86 * so if the user is interested in a signal, that corresponding
87 * bit will be zero.
88 */
89 if (sig < 0) {
90 if (ctx->tsk == tsk) {
91 ctx->tsk = NULL;
92 list_del_init(&ctx->lnk);
93 wake_up(&ctx->wqh);
94 }
95 } else {
96 if (!sigismember(&ctx->sigmask, sig))
97 wake_up(&ctx->wqh);
98 }
99 }
100}
101
102static void signalfd_cleanup(struct signalfd_ctx *ctx)
103{
104 struct signalfd_lockctx lk;
105
106 /*
107 * This is tricky. If the sighand is gone, we do not need to remove
108 * context from the list, the list itself won't be there anymore.
109 */
110 if (signalfd_lock(ctx, &lk)) {
111 list_del(&ctx->lnk);
112 signalfd_unlock(&lk);
113 }
114 kfree(ctx);
115}
116
117static int signalfd_release(struct inode *inode, struct file *file)
118{
119 signalfd_cleanup(file->private_data);
120 return 0;
121}
122
123static unsigned int signalfd_poll(struct file *file, poll_table *wait)
124{
125 struct signalfd_ctx *ctx = file->private_data;
126 unsigned int events = 0;
127 struct signalfd_lockctx lk;
128
129 poll_wait(file, &ctx->wqh, wait);
130
131 /*
132 * Let the caller get a POLLIN in this case, ala socket recv() when
133 * the peer disconnects.
134 */
135 if (signalfd_lock(ctx, &lk)) {
Davide Libenzif8738c52007-06-27 14:09:59 -0700136 if ((lk.tsk == current &&
137 next_signal(&lk.tsk->pending, &ctx->sigmask) > 0) ||
Davide Libenzifba2afa2007-05-10 22:23:13 -0700138 next_signal(&lk.tsk->signal->shared_pending,
139 &ctx->sigmask) > 0)
140 events |= POLLIN;
141 signalfd_unlock(&lk);
142 } else
143 events |= POLLIN;
144
145 return events;
146}
147
148/*
149 * Copied from copy_siginfo_to_user() in kernel/signal.c
150 */
151static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
152 siginfo_t const *kinfo)
153{
154 long err;
155
156 BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
157
158 /*
159 * Unused memebers should be zero ...
160 */
161 err = __clear_user(uinfo, sizeof(*uinfo));
162
163 /*
164 * If you change siginfo_t structure, please be sure
165 * this code is fixed accordingly.
166 */
167 err |= __put_user(kinfo->si_signo, &uinfo->signo);
168 err |= __put_user(kinfo->si_errno, &uinfo->err);
169 err |= __put_user((short)kinfo->si_code, &uinfo->code);
170 switch (kinfo->si_code & __SI_MASK) {
171 case __SI_KILL:
172 err |= __put_user(kinfo->si_pid, &uinfo->pid);
173 err |= __put_user(kinfo->si_uid, &uinfo->uid);
174 break;
175 case __SI_TIMER:
176 err |= __put_user(kinfo->si_tid, &uinfo->tid);
177 err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
178 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
179 break;
180 case __SI_POLL:
181 err |= __put_user(kinfo->si_band, &uinfo->band);
182 err |= __put_user(kinfo->si_fd, &uinfo->fd);
183 break;
184 case __SI_FAULT:
185 err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
186#ifdef __ARCH_SI_TRAPNO
187 err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
188#endif
189 break;
190 case __SI_CHLD:
191 err |= __put_user(kinfo->si_pid, &uinfo->pid);
192 err |= __put_user(kinfo->si_uid, &uinfo->uid);
193 err |= __put_user(kinfo->si_status, &uinfo->status);
194 err |= __put_user(kinfo->si_utime, &uinfo->utime);
195 err |= __put_user(kinfo->si_stime, &uinfo->stime);
196 break;
197 case __SI_RT: /* This is not generated by the kernel as of now. */
198 case __SI_MESGQ: /* But this is */
199 err |= __put_user(kinfo->si_pid, &uinfo->pid);
200 err |= __put_user(kinfo->si_uid, &uinfo->uid);
201 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
202 break;
203 default: /* this is just in case for now ... */
204 err |= __put_user(kinfo->si_pid, &uinfo->pid);
205 err |= __put_user(kinfo->si_uid, &uinfo->uid);
206 break;
207 }
208
209 return err ? -EFAULT: sizeof(*uinfo);
210}
211
Davi Arnautb3762bf2007-05-23 13:58:04 -0700212static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
213 int nonblock)
214{
215 ssize_t ret;
216 struct signalfd_lockctx lk;
217 DECLARE_WAITQUEUE(wait, current);
218
219 if (!signalfd_lock(ctx, &lk))
220 return 0;
221
222 ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
223 switch (ret) {
224 case 0:
225 if (!nonblock)
226 break;
227 ret = -EAGAIN;
228 default:
229 signalfd_unlock(&lk);
230 return ret;
231 }
232
233 add_wait_queue(&ctx->wqh, &wait);
234 for (;;) {
235 set_current_state(TASK_INTERRUPTIBLE);
236 ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
237 signalfd_unlock(&lk);
238 if (ret != 0)
239 break;
240 if (signal_pending(current)) {
241 ret = -ERESTARTSYS;
242 break;
243 }
244 schedule();
245 ret = signalfd_lock(ctx, &lk);
246 if (unlikely(!ret)) {
247 /*
248 * Let the caller read zero byte, ala socket
249 * recv() when the peer disconnect. This test
250 * must be done before doing a dequeue_signal(),
251 * because if the sighand has been orphaned,
252 * the dequeue_signal() call is going to crash
253 * because ->sighand will be long gone.
254 */
255 break;
256 }
257 }
258
259 remove_wait_queue(&ctx->wqh, &wait);
260 __set_current_state(TASK_RUNNING);
261
262 return ret;
263}
264
Davide Libenzifba2afa2007-05-10 22:23:13 -0700265/*
266 * Returns either the size of a "struct signalfd_siginfo", or zero if the
267 * sighand we are attached to, has been orphaned. The "count" parameter
268 * must be at least the size of a "struct signalfd_siginfo".
269 */
270static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
271 loff_t *ppos)
272{
273 struct signalfd_ctx *ctx = file->private_data;
Davi Arnautb3762bf2007-05-23 13:58:04 -0700274 struct signalfd_siginfo __user *siginfo;
275 int nonblock = file->f_flags & O_NONBLOCK;
276 ssize_t ret, total = 0;
Davide Libenzifba2afa2007-05-10 22:23:13 -0700277 siginfo_t info;
Davide Libenzifba2afa2007-05-10 22:23:13 -0700278
Davi Arnautb3762bf2007-05-23 13:58:04 -0700279 count /= sizeof(struct signalfd_siginfo);
280 if (!count)
Davide Libenzifba2afa2007-05-10 22:23:13 -0700281 return -EINVAL;
Davide Libenzifba2afa2007-05-10 22:23:13 -0700282
Davi Arnautb3762bf2007-05-23 13:58:04 -0700283 siginfo = (struct signalfd_siginfo __user *) buf;
284
285 do {
286 ret = signalfd_dequeue(ctx, &info, nonblock);
287 if (unlikely(ret <= 0))
288 break;
289 ret = signalfd_copyinfo(siginfo, &info);
290 if (ret < 0)
291 break;
292 siginfo++;
293 total += ret;
294 nonblock = 1;
295 } while (--count);
296
297 return total ? total : ret;
Davide Libenzifba2afa2007-05-10 22:23:13 -0700298}
299
300static const struct file_operations signalfd_fops = {
301 .release = signalfd_release,
302 .poll = signalfd_poll,
303 .read = signalfd_read,
304};
305
306/*
307 * Create a file descriptor that is associated with our signal
308 * state. We can pass it around to others if we want to, but
309 * it will always be _our_ signal state.
310 */
311asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
312{
313 int error;
314 sigset_t sigmask;
315 struct signalfd_ctx *ctx;
316 struct sighand_struct *sighand;
317 struct file *file;
318 struct inode *inode;
319 struct signalfd_lockctx lk;
320
321 if (sizemask != sizeof(sigset_t) ||
322 copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
323 return error = -EINVAL;
324 sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
325 signotset(&sigmask);
326
327 if (ufd == -1) {
328 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
329 if (!ctx)
330 return -ENOMEM;
331
332 init_waitqueue_head(&ctx->wqh);
333 ctx->sigmask = sigmask;
334 ctx->tsk = current;
335
336 sighand = current->sighand;
337 /*
338 * Add this fd to the list of signal listeners.
339 */
340 spin_lock_irq(&sighand->siglock);
341 list_add_tail(&ctx->lnk, &sighand->signalfd_list);
342 spin_unlock_irq(&sighand->siglock);
343
344 /*
345 * When we call this, the initialization must be complete, since
346 * anon_inode_getfd() will install the fd.
347 */
348 error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
349 &signalfd_fops, ctx);
350 if (error)
351 goto err_fdalloc;
352 } else {
353 file = fget(ufd);
354 if (!file)
355 return -EBADF;
356 ctx = file->private_data;
357 if (file->f_op != &signalfd_fops) {
358 fput(file);
359 return -EINVAL;
360 }
361 /*
362 * We need to be prepared of the fact that the sighand this fd
363 * is attached to, has been detched. In that case signalfd_lock()
364 * will return 0, and we'll just skip setting the new mask.
365 */
366 if (signalfd_lock(ctx, &lk)) {
367 ctx->sigmask = sigmask;
368 signalfd_unlock(&lk);
369 }
370 wake_up(&ctx->wqh);
371 fput(file);
372 }
373
374 return ufd;
375
376err_fdalloc:
377 signalfd_cleanup(ctx);
378 return error;
379}
380