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349 lines
9.1 KiB
349 lines
9.1 KiB
/*
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* fs/signalfd.c
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*
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* Copyright (C) 2003 Linus Torvalds
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*
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* Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
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* Changed ->read() to return a siginfo strcture instead of signal number.
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* Fixed locking in ->poll().
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* Added sighand-detach notification.
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* Added fd re-use in sys_signalfd() syscall.
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* Now using anonymous inode source.
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* Thanks to Oleg Nesterov for useful code review and suggestions.
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* More comments and suggestions from Arnd Bergmann.
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*/
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#include <linux/file.h>
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#include <linux/poll.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/signal.h>
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#include <linux/list.h>
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#include <linux/anon_inodes.h>
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#include <linux/signalfd.h>
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struct signalfd_ctx {
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struct list_head lnk;
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wait_queue_head_t wqh;
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sigset_t sigmask;
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struct task_struct *tsk;
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};
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struct signalfd_lockctx {
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struct task_struct *tsk;
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unsigned long flags;
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};
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/*
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* Tries to acquire the sighand lock. We do not increment the sighand
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* use count, and we do not even pin the task struct, so we need to
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* do it inside an RCU read lock, and we must be prepared for the
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* ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
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* being detached. We return 0 if the sighand has been detached, or
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* 1 if we were able to pin the sighand lock.
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*/
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static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
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{
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struct sighand_struct *sighand = NULL;
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rcu_read_lock();
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lk->tsk = rcu_dereference(ctx->tsk);
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if (likely(lk->tsk != NULL))
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sighand = lock_task_sighand(lk->tsk, &lk->flags);
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rcu_read_unlock();
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if (sighand && !ctx->tsk) {
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unlock_task_sighand(lk->tsk, &lk->flags);
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sighand = NULL;
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}
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return sighand != NULL;
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}
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static void signalfd_unlock(struct signalfd_lockctx *lk)
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{
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unlock_task_sighand(lk->tsk, &lk->flags);
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}
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/*
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* This must be called with the sighand lock held.
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*/
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void signalfd_deliver(struct task_struct *tsk, int sig)
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{
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struct sighand_struct *sighand = tsk->sighand;
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struct signalfd_ctx *ctx, *tmp;
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BUG_ON(!sig);
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list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
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/*
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* We use a negative signal value as a way to broadcast that the
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* sighand has been orphaned, so that we can notify all the
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* listeners about this. Remember the ctx->sigmask is inverted,
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* so if the user is interested in a signal, that corresponding
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* bit will be zero.
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*/
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if (sig < 0) {
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if (ctx->tsk == tsk) {
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ctx->tsk = NULL;
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list_del_init(&ctx->lnk);
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wake_up(&ctx->wqh);
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}
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} else {
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if (!sigismember(&ctx->sigmask, sig))
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wake_up(&ctx->wqh);
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}
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}
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}
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static void signalfd_cleanup(struct signalfd_ctx *ctx)
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{
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struct signalfd_lockctx lk;
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/*
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* This is tricky. If the sighand is gone, we do not need to remove
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* context from the list, the list itself won't be there anymore.
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*/
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if (signalfd_lock(ctx, &lk)) {
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list_del(&ctx->lnk);
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signalfd_unlock(&lk);
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}
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kfree(ctx);
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}
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static int signalfd_release(struct inode *inode, struct file *file)
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{
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signalfd_cleanup(file->private_data);
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return 0;
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}
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static unsigned int signalfd_poll(struct file *file, poll_table *wait)
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{
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struct signalfd_ctx *ctx = file->private_data;
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unsigned int events = 0;
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struct signalfd_lockctx lk;
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poll_wait(file, &ctx->wqh, wait);
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/*
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* Let the caller get a POLLIN in this case, ala socket recv() when
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* the peer disconnects.
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*/
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if (signalfd_lock(ctx, &lk)) {
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if (next_signal(&lk.tsk->pending, &ctx->sigmask) > 0 ||
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next_signal(&lk.tsk->signal->shared_pending,
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&ctx->sigmask) > 0)
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events |= POLLIN;
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signalfd_unlock(&lk);
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} else
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events |= POLLIN;
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return events;
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}
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/*
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* Copied from copy_siginfo_to_user() in kernel/signal.c
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*/
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static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
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siginfo_t const *kinfo)
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{
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long err;
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BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
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/*
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* Unused memebers should be zero ...
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*/
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err = __clear_user(uinfo, sizeof(*uinfo));
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/*
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* If you change siginfo_t structure, please be sure
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* this code is fixed accordingly.
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*/
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err |= __put_user(kinfo->si_signo, &uinfo->signo);
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err |= __put_user(kinfo->si_errno, &uinfo->err);
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err |= __put_user((short)kinfo->si_code, &uinfo->code);
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switch (kinfo->si_code & __SI_MASK) {
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case __SI_KILL:
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err |= __put_user(kinfo->si_pid, &uinfo->pid);
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err |= __put_user(kinfo->si_uid, &uinfo->uid);
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break;
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case __SI_TIMER:
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err |= __put_user(kinfo->si_tid, &uinfo->tid);
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err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
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err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
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break;
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case __SI_POLL:
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err |= __put_user(kinfo->si_band, &uinfo->band);
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err |= __put_user(kinfo->si_fd, &uinfo->fd);
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break;
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case __SI_FAULT:
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err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
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#ifdef __ARCH_SI_TRAPNO
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err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
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#endif
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break;
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case __SI_CHLD:
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err |= __put_user(kinfo->si_pid, &uinfo->pid);
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err |= __put_user(kinfo->si_uid, &uinfo->uid);
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err |= __put_user(kinfo->si_status, &uinfo->status);
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err |= __put_user(kinfo->si_utime, &uinfo->utime);
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err |= __put_user(kinfo->si_stime, &uinfo->stime);
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break;
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case __SI_RT: /* This is not generated by the kernel as of now. */
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case __SI_MESGQ: /* But this is */
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err |= __put_user(kinfo->si_pid, &uinfo->pid);
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err |= __put_user(kinfo->si_uid, &uinfo->uid);
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err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
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break;
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default: /* this is just in case for now ... */
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err |= __put_user(kinfo->si_pid, &uinfo->pid);
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err |= __put_user(kinfo->si_uid, &uinfo->uid);
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break;
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}
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return err ? -EFAULT: sizeof(*uinfo);
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}
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/*
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* Returns either the size of a "struct signalfd_siginfo", or zero if the
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* sighand we are attached to, has been orphaned. The "count" parameter
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* must be at least the size of a "struct signalfd_siginfo".
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*/
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static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
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loff_t *ppos)
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{
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struct signalfd_ctx *ctx = file->private_data;
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ssize_t res = 0;
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int locked, signo;
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siginfo_t info;
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struct signalfd_lockctx lk;
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DECLARE_WAITQUEUE(wait, current);
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if (count < sizeof(struct signalfd_siginfo))
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return -EINVAL;
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locked = signalfd_lock(ctx, &lk);
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if (!locked)
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return 0;
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res = -EAGAIN;
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signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
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if (signo == 0 && !(file->f_flags & O_NONBLOCK)) {
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add_wait_queue(&ctx->wqh, &wait);
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for (;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
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if (signo != 0)
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break;
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if (signal_pending(current)) {
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res = -ERESTARTSYS;
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break;
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}
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signalfd_unlock(&lk);
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schedule();
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locked = signalfd_lock(ctx, &lk);
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if (unlikely(!locked)) {
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/*
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* Let the caller read zero byte, ala socket
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* recv() when the peer disconnect. This test
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* must be done before doing a dequeue_signal(),
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* because if the sighand has been orphaned,
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* the dequeue_signal() call is going to crash.
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*/
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res = 0;
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break;
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}
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}
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remove_wait_queue(&ctx->wqh, &wait);
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__set_current_state(TASK_RUNNING);
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}
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if (likely(locked))
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signalfd_unlock(&lk);
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if (likely(signo))
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res = signalfd_copyinfo((struct signalfd_siginfo __user *) buf,
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&info);
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return res;
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}
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static const struct file_operations signalfd_fops = {
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.release = signalfd_release,
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.poll = signalfd_poll,
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.read = signalfd_read,
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};
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/*
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* Create a file descriptor that is associated with our signal
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* state. We can pass it around to others if we want to, but
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* it will always be _our_ signal state.
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*/
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asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
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{
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int error;
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sigset_t sigmask;
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struct signalfd_ctx *ctx;
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struct sighand_struct *sighand;
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struct file *file;
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struct inode *inode;
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struct signalfd_lockctx lk;
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if (sizemask != sizeof(sigset_t) ||
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copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
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return error = -EINVAL;
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sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
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signotset(&sigmask);
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if (ufd == -1) {
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return -ENOMEM;
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init_waitqueue_head(&ctx->wqh);
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ctx->sigmask = sigmask;
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ctx->tsk = current;
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sighand = current->sighand;
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/*
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* Add this fd to the list of signal listeners.
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*/
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spin_lock_irq(&sighand->siglock);
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list_add_tail(&ctx->lnk, &sighand->signalfd_list);
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spin_unlock_irq(&sighand->siglock);
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/*
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* When we call this, the initialization must be complete, since
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* anon_inode_getfd() will install the fd.
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*/
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error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
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&signalfd_fops, ctx);
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if (error)
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goto err_fdalloc;
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} else {
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file = fget(ufd);
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if (!file)
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return -EBADF;
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ctx = file->private_data;
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if (file->f_op != &signalfd_fops) {
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fput(file);
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return -EINVAL;
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}
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/*
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* We need to be prepared of the fact that the sighand this fd
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* is attached to, has been detched. In that case signalfd_lock()
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* will return 0, and we'll just skip setting the new mask.
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*/
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if (signalfd_lock(ctx, &lk)) {
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ctx->sigmask = sigmask;
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signalfd_unlock(&lk);
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}
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wake_up(&ctx->wqh);
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fput(file);
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}
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return ufd;
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err_fdalloc:
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signalfd_cleanup(ctx);
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return error;
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}
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