3 files changed, 359 insertions, 2 deletions

diff --git a/fs/Makefile b/fs/Makefile
index b5cd46a88cb0..cd8a57aeac04 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -23,6 +23,7 @@ obj-$(CONFIG_INOTIFY)		+= inotify.o
 obj-$(CONFIG_INOTIFY_USER)      += inotify_user.o
 obj-$(CONFIG_EPOLL)             += eventpoll.o
 obj-$(CONFIG_ANON_INODES)       += anon_inodes.o
+obj-$(CONFIG_SIGNALFD)          += signalfd.o
 obj-$(CONFIG_COMPAT)            += compat.o compat_ioctl.o
 
 nfsd-$(CONFIG_NFSD)             := nfsctl.o
diff --git a/fs/exec.c b/fs/exec.c
index 2255dc72deef..955a8eb66d70 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -50,6 +50,7 @@
 #include <linux/tsacct_kern.h>
 #include <linux/cn_proc.h>
 #include <linux/audit.h>
+#include <linux/signalfd.h>
 
 #include <asm/uaccess.h>
 #include <asm/mmu_context.h>
@@ -582,6 +583,13 @@ static int de_thread(struct task_struct *tsk)
         int count;
 
         /*
+         * Tell all the sighand listeners that this sighand has
+         * been detached. The signalfd_detach() function grabs the
+         * sighand lock, if signal listeners are present on the sighand.
+         */
+        signalfd_detach(tsk);
+
+        /*
          * If we don't share sighandlers, then we aren't sharing anything
          * and we can just re-use it all.
          */
@@ -757,8 +765,7 @@ no_thread_group:
                 spin_unlock(&oldsighand->siglock);
                 write_unlock_irq(&tasklist_lock);
 
-                if (atomic_dec_and_test(&oldsighand->count))
-                        kmem_cache_free(sighand_cachep, oldsighand);
+                __cleanup_sighand(oldsighand);
         }
 
         BUG_ON(!thread_group_leader(tsk));
diff --git a/fs/signalfd.c b/fs/signalfd.c
new file mode 100644
index 000000000000..7cfeab412b45
--- /dev/null
+++ b/fs/signalfd.c
@@ -0,0 +1,349 @@
+/*
+ *  fs/signalfd.c
+ *
+ *  Copyright (C) 2003  Linus Torvalds
+ *
+ *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
+ *      Changed ->read() to return a siginfo strcture instead of signal number.
+ *      Fixed locking in ->poll().
+ *      Added sighand-detach notification.
+ *      Added fd re-use in sys_signalfd() syscall.
+ *      Now using anonymous inode source.
+ *      Thanks to Oleg Nesterov for useful code review and suggestions.
+ *      More comments and suggestions from Arnd Bergmann.
+ */
+
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/signal.h>
+#include <linux/list.h>
+#include <linux/anon_inodes.h>
+#include <linux/signalfd.h>
+
+struct signalfd_ctx {
+        struct list_head lnk;
+        wait_queue_head_t wqh;
+        sigset_t sigmask;
+        struct task_struct *tsk;
+};
+
+struct signalfd_lockctx {
+        struct task_struct *tsk;
+        unsigned long flags;
+};
+
+/*
+ * Tries to acquire the sighand lock. We do not increment the sighand
+ * use count, and we do not even pin the task struct, so we need to
+ * do it inside an RCU read lock, and we must be prepared for the
+ * ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
+ * being detached. We return 0 if the sighand has been detached, or
+ * 1 if we were able to pin the sighand lock.
+ */
+static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
+{
+        struct sighand_struct *sighand = NULL;
+
+        rcu_read_lock();
+        lk->tsk = rcu_dereference(ctx->tsk);
+        if (likely(lk->tsk != NULL))
+                sighand = lock_task_sighand(lk->tsk, &lk->flags);
+        rcu_read_unlock();
+
+        if (sighand && !ctx->tsk) {
+                unlock_task_sighand(lk->tsk, &lk->flags);
+                sighand = NULL;
+        }
+
+        return sighand != NULL;
+}
+
+static void signalfd_unlock(struct signalfd_lockctx *lk)
+{
+        unlock_task_sighand(lk->tsk, &lk->flags);
+}
+
+/*
+ * This must be called with the sighand lock held.
+ */
+void signalfd_deliver(struct task_struct *tsk, int sig)
+{
+        struct sighand_struct *sighand = tsk->sighand;
+        struct signalfd_ctx *ctx, *tmp;
+
+        BUG_ON(!sig);
+        list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
+                /*
+                 * We use a negative signal value as a way to broadcast that the
+                 * sighand has been orphaned, so that we can notify all the
+                 * listeners about this. Remember the ctx->sigmask is inverted,
+                 * so if the user is interested in a signal, that corresponding
+                 * bit will be zero.
+                 */
+                if (sig < 0) {
+                        if (ctx->tsk == tsk) {
+                                ctx->tsk = NULL;
+                                list_del_init(&ctx->lnk);
+                                wake_up(&ctx->wqh);
+                        }
+                } else {
+                        if (!sigismember(&ctx->sigmask, sig))
+                                wake_up(&ctx->wqh);
+                }
+        }
+}
+
+static void signalfd_cleanup(struct signalfd_ctx *ctx)
+{
+        struct signalfd_lockctx lk;
+
+        /*
+         * This is tricky. If the sighand is gone, we do not need to remove
+         * context from the list, the list itself won't be there anymore.
+         */
+        if (signalfd_lock(ctx, &lk)) {
+                list_del(&ctx->lnk);
+                signalfd_unlock(&lk);
+        }
+        kfree(ctx);
+}
+
+static int signalfd_release(struct inode *inode, struct file *file)
+{
+        signalfd_cleanup(file->private_data);
+        return 0;
+}
+
+static unsigned int signalfd_poll(struct file *file, poll_table *wait)
+{
+        struct signalfd_ctx *ctx = file->private_data;
+        unsigned int events = 0;
+        struct signalfd_lockctx lk;
+
+        poll_wait(file, &ctx->wqh, wait);
+
+        /*
+         * Let the caller get a POLLIN in this case, ala socket recv() when
+         * the peer disconnects.
+         */
+        if (signalfd_lock(ctx, &lk)) {
+                if (next_signal(&lk.tsk->pending, &ctx->sigmask) > 0 ||
+                    next_signal(&lk.tsk->signal->shared_pending,
+                                &ctx->sigmask) > 0)
+                        events |= POLLIN;
+                signalfd_unlock(&lk);
+        } else
+                events |= POLLIN;
+
+        return events;
+}
+
+/*
+ * Copied from copy_siginfo_to_user() in kernel/signal.c
+ */
+static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
+                             siginfo_t const *kinfo)
+{
+        long err;
+
+        BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
+
+        /*
+         * Unused memebers should be zero ...
+         */
+        err = __clear_user(uinfo, sizeof(*uinfo));
+
+        /*
+         * If you change siginfo_t structure, please be sure
+         * this code is fixed accordingly.
+         */
+        err |= __put_user(kinfo->si_signo, &uinfo->signo);
+        err |= __put_user(kinfo->si_errno, &uinfo->err);
+        err |= __put_user((short)kinfo->si_code, &uinfo->code);
+        switch (kinfo->si_code & __SI_MASK) {
+        case __SI_KILL:
+                err |= __put_user(kinfo->si_pid, &uinfo->pid);
+                err |= __put_user(kinfo->si_uid, &uinfo->uid);
+                break;
+        case __SI_TIMER:
+                 err |= __put_user(kinfo->si_tid, &uinfo->tid);
+                 err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
+                 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
+                break;
+        case __SI_POLL:
+                err |= __put_user(kinfo->si_band, &uinfo->band);
+                err |= __put_user(kinfo->si_fd, &uinfo->fd);
+                break;
+        case __SI_FAULT:
+                err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
+#ifdef __ARCH_SI_TRAPNO
+                err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
+#endif
+                break;
+        case __SI_CHLD:
+                err |= __put_user(kinfo->si_pid, &uinfo->pid);
+                err |= __put_user(kinfo->si_uid, &uinfo->uid);
+                err |= __put_user(kinfo->si_status, &uinfo->status);
+                err |= __put_user(kinfo->si_utime, &uinfo->utime);
+                err |= __put_user(kinfo->si_stime, &uinfo->stime);
+                break;
+        case __SI_RT: /* This is not generated by the kernel as of now. */
+        case __SI_MESGQ: /* But this is */
+                err |= __put_user(kinfo->si_pid, &uinfo->pid);
+                err |= __put_user(kinfo->si_uid, &uinfo->uid);
+                err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
+                break;
+        default: /* this is just in case for now ... */
+                err |= __put_user(kinfo->si_pid, &uinfo->pid);
+                err |= __put_user(kinfo->si_uid, &uinfo->uid);
+                break;
+        }
+
+        return err ? -EFAULT: sizeof(*uinfo);
+}
+
+/*
+ * Returns either the size of a "struct signalfd_siginfo", or zero if the
+ * sighand we are attached to, has been orphaned. The "count" parameter
+ * must be at least the size of a "struct signalfd_siginfo".
+ */
+static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
+                             loff_t *ppos)
+{
+        struct signalfd_ctx *ctx = file->private_data;
+        ssize_t res = 0;
+        int locked, signo;
+        siginfo_t info;
+        struct signalfd_lockctx lk;
+        DECLARE_WAITQUEUE(wait, current);
+
+        if (count < sizeof(struct signalfd_siginfo))
+                return -EINVAL;
+        locked = signalfd_lock(ctx, &lk);
+        if (!locked)
+                return 0;
+        res = -EAGAIN;
+        signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
+        if (signo == 0 && !(file->f_flags & O_NONBLOCK)) {
+                add_wait_queue(&ctx->wqh, &wait);
+                for (;;) {
+                        set_current_state(TASK_INTERRUPTIBLE);
+                        signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
+                        if (signo != 0)
+                                break;
+                        if (signal_pending(current)) {
+                                res = -ERESTARTSYS;
+                                break;
+                        }
+                        signalfd_unlock(&lk);
+                        schedule();
+                        locked = signalfd_lock(ctx, &lk);
+                        if (unlikely(!locked)) {
+                                /*
+                                 * Let the caller read zero byte, ala socket
+                                 * recv() when the peer disconnect. This test
+                                 * must be done before doing a dequeue_signal(),
+                                 * because if the sighand has been orphaned,
+                                 * the dequeue_signal() call is going to crash.
+                                 */
+                                res = 0;
+                                break;
+                        }
+                }
+                remove_wait_queue(&ctx->wqh, &wait);
+                __set_current_state(TASK_RUNNING);
+        }
+        if (likely(locked))
+                signalfd_unlock(&lk);
+        if (likely(signo))
+                res = signalfd_copyinfo((struct signalfd_siginfo __user *) buf,
+                                        &info);
+
+        return res;
+}
+
+static const struct file_operations signalfd_fops = {
+        .release        = signalfd_release,
+        .poll           = signalfd_poll,
+        .read           = signalfd_read,
+};
+
+/*
+ * Create a file descriptor that is associated with our signal
+ * state. We can pass it around to others if we want to, but
+ * it will always be _our_ signal state.
+ */
+asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
+{
+        int error;
+        sigset_t sigmask;
+        struct signalfd_ctx *ctx;
+        struct sighand_struct *sighand;
+        struct file *file;
+        struct inode *inode;
+        struct signalfd_lockctx lk;
+
+        if (sizemask != sizeof(sigset_t) ||
+            copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
+                return error = -EINVAL;
+        sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
+        signotset(&sigmask);
+
+        if (ufd == -1) {
+                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+                if (!ctx)
+                        return -ENOMEM;
+
+                init_waitqueue_head(&ctx->wqh);
+                ctx->sigmask = sigmask;
+                ctx->tsk = current;
+
+                sighand = current->sighand;
+                /*
+                 * Add this fd to the list of signal listeners.
+                 */
+                spin_lock_irq(&sighand->siglock);
+                list_add_tail(&ctx->lnk, &sighand->signalfd_list);
+                spin_unlock_irq(&sighand->siglock);
+
+                /*
+                 * When we call this, the initialization must be complete, since
+                 * anon_inode_getfd() will install the fd.
+                 */
+                error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
+                                         &signalfd_fops, ctx);
+                if (error)
+                        goto err_fdalloc;
+        } else {
+                file = fget(ufd);
+                if (!file)
+                        return -EBADF;
+                ctx = file->private_data;
+                if (file->f_op != &signalfd_fops) {
+                        fput(file);
+                        return -EINVAL;
+                }
+                /*
+                 * We need to be prepared of the fact that the sighand this fd
+                 * is attached to, has been detched. In that case signalfd_lock()
+                 * will return 0, and we'll just skip setting the new mask.
+                 */
+                if (signalfd_lock(ctx, &lk)) {
+                        ctx->sigmask = sigmask;
+                        signalfd_unlock(&lk);
+                }
+                wake_up(&ctx->wqh);
+                fput(file);
+        }
+
+        return ufd;
+
+err_fdalloc:
+        signalfd_cleanup(ctx);
+        return error;
+}
+