1 files changed, 29 insertions, 161 deletions

diff --git a/fs/signalfd.c b/fs/signalfd.c
index a8e293d30034..aefb0be07942 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;
 }