1 files changed, 29 insertions, 161 deletions

diff --git a/fs/signalfd.c b/fs/signalfd.c
index a8e293d..aefb0be 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -11,8 +11,10 @@
  *      Now using anonymous inode source.
  *      Thanks to Oleg Nesterov for useful code review and suggestions.
  *      More comments and suggestions from Arnd Bergmann.
- * Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
+ *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
  *      Retrieve multiple signals with one read() call
+ *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
+ *      Attach to the sighand only during read() and poll().
  */
 
 #include <linux/file.h>
@@ -27,102 +29,12 @@
 #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)
-		return 0;
-
-	if (!ctx->tsk) {
-		unlock_task_sighand(lk->tsk, &lk->flags);
-		return 0;
-	}
-
-	if (lk->tsk->tgid == current->tgid)
-		lk->tsk = current;
-
-	return 1;
-}
-
-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);
+	kfree(file->private_data);
 	return 0;
 }
 
@@ -130,23 +42,15 @@ 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);
+	poll_wait(file, &current->sighand->signalfd_wqh, wait);
 
-	/*
-	 * Let the caller get a POLLIN in this case, ala socket recv() when
-	 * the peer disconnects.
-	 */
-	if (signalfd_lock(ctx, &lk)) {
-		if ((lk.tsk == current &&
-		     next_signal(&lk.tsk->pending, &ctx->sigmask) > 0) ||
-		    next_signal(&lk.tsk->signal->shared_pending,
-				&ctx->sigmask) > 0)
-			events |= POLLIN;
-		signalfd_unlock(&lk);
-	} else
+	spin_lock_irq(&current->sighand->siglock);
+	if (next_signal(&current->pending, &ctx->sigmask) ||
+	    next_signal(&current->signal->shared_pending,
+			&ctx->sigmask))
 		events |= POLLIN;
+	spin_unlock_irq(&current->sighand->siglock);
 
 	return events;
 }
@@ -219,59 +123,46 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 				int nonblock)
 {
 	ssize_t ret;
-	struct signalfd_lockctx lk;
 	DECLARE_WAITQUEUE(wait, current);
 
-	if (!signalfd_lock(ctx, &lk))
-		return 0;
-
-	ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
+	spin_lock_irq(&current->sighand->siglock);
+	ret = dequeue_signal(current, &ctx->sigmask, info);
 	switch (ret) {
 	case 0:
 		if (!nonblock)
 			break;
 		ret = -EAGAIN;
 	default:
-		signalfd_unlock(&lk);
+		spin_unlock_irq(&current->sighand->siglock);
 		return ret;
 	}
 
-	add_wait_queue(&ctx->wqh, &wait);
+	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
-		ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
-		signalfd_unlock(&lk);
+		ret = dequeue_signal(current, &ctx->sigmask, info);
 		if (ret != 0)
 			break;
 		if (signal_pending(current)) {
 			ret = -ERESTARTSYS;
 			break;
 		}
+		spin_unlock_irq(&current->sighand->siglock);
 		schedule();
-		ret = signalfd_lock(ctx, &lk);
-		if (unlikely(!ret)) {
-			/*
-			 * 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
-			 * because ->sighand will be long gone.
-			 */
-			 break;
-		}
+		spin_lock_irq(&current->sighand->siglock);
 	}
+	spin_unlock_irq(&current->sighand->siglock);
 
-	remove_wait_queue(&ctx->wqh, &wait);
+	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 	__set_current_state(TASK_RUNNING);
 
 	return ret;
 }
 
 /*
- * 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".
+ * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
+ * error code. 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)
@@ -287,7 +178,6 @@ static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 		return -EINVAL;
 
 	siginfo = (struct signalfd_siginfo __user *) buf;
-
 	do {
 		ret = signalfd_dequeue(ctx, &info, nonblock);
 		if (unlikely(ret <= 0))
@@ -300,7 +190,7 @@ static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 		nonblock = 1;
 	} while (--count);
 
-	return total ? total : ret;
+	return total ? total: ret;
 }
 
 static const struct file_operations signalfd_fops = {
@@ -309,20 +199,13 @@ static const struct file_operations signalfd_fops = {
 	.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)))
@@ -335,17 +218,7 @@ asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemas
 		if (!ctx)
 			return -ENOMEM;
 
-		init_waitqueue_head(&ctx->wqh);
 		ctx->sigmask = sigmask;
-		ctx->tsk = current->group_leader;
-
-		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
@@ -364,23 +237,18 @@ asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemas
 			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);
+		spin_lock_irq(&current->sighand->siglock);
+		ctx->sigmask = sigmask;
+		spin_unlock_irq(&current->sighand->siglock);
+
+		wake_up(&current->sighand->signalfd_wqh);
 		fput(file);
 	}
 
 	return ufd;
 
 err_fdalloc:
-	signalfd_cleanup(ctx);
+	kfree(ctx);
 	return error;
 }