* 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>
#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;
}
{
struct signalfd_ctx *ctx = file->private_data;
unsigned int events = 0;
- struct signalfd_lockctx lk;
- poll_wait(file, &ctx->wqh, wait);
+ poll_wait(file, ¤t->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(¤t->sighand->siglock);
+ if (next_signal(¤t->pending, &ctx->sigmask) ||
+ next_signal(¤t->signal->shared_pending,
+ &ctx->sigmask))
events |= POLLIN;
+ spin_unlock_irq(¤t->sighand->siglock);
return events;
}
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(¤t->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(¤t->sighand->siglock);
return ret;
}
- add_wait_queue(&ctx->wqh, &wait);
+ add_wait_queue(¤t->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(¤t->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(¤t->sighand->siglock);
}
+ spin_unlock_irq(¤t->sighand->siglock);
- remove_wait_queue(&ctx->wqh, &wait);
+ remove_wait_queue(¤t->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)
return -EINVAL;
siginfo = (struct signalfd_siginfo __user *) buf;
-
do {
ret = signalfd_dequeue(ctx, &info, nonblock);
if (unlikely(ret <= 0))
nonblock = 1;
} while (--count);
- return total ? total : ret;
+ return total ? total: ret;
}
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)))
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
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(¤t->sighand->siglock);
+ ctx->sigmask = sigmask;
+ spin_unlock_irq(¤t->sighand->siglock);
+
+ wake_up(¤t->sighand->signalfd_wqh);
fput(file);
}
return ufd;
err_fdalloc:
- signalfd_cleanup(ctx);
+ kfree(ctx);
return error;
}
#ifdef CONFIG_SIGNALFD
/*
- * Deliver the signal to listening signalfd. This must be called
- * with the sighand lock held. Same are the following that end up
- * calling signalfd_deliver().
- */
-void signalfd_deliver(struct task_struct *tsk, int sig);
-
-/*
- * No need to fall inside signalfd_deliver() if no signal listeners
- * are available.
+ * Deliver the signal to listening signalfd.
*/
static inline void signalfd_notify(struct task_struct *tsk, int sig)
{
- if (unlikely(!list_empty(&tsk->sighand->signalfd_list)))
- signalfd_deliver(tsk, sig);
-}
-
-/*
- * The signal -1 is used to notify the signalfd that the sighand
- * is on its way to be detached.
- */
-static inline void signalfd_detach_locked(struct task_struct *tsk)
-{
- if (unlikely(!list_empty(&tsk->sighand->signalfd_list)))
- signalfd_deliver(tsk, -1);
-}
-
-static inline void signalfd_detach(struct task_struct *tsk)
-{
- struct sighand_struct *sighand = tsk->sighand;
-
- if (unlikely(!list_empty(&sighand->signalfd_list))) {
- spin_lock_irq(&sighand->siglock);
- signalfd_deliver(tsk, -1);
- spin_unlock_irq(&sighand->siglock);
- }
+ if (unlikely(waitqueue_active(&tsk->sighand->signalfd_wqh)))
+ wake_up(&tsk->sighand->signalfd_wqh);
}
#else /* CONFIG_SIGNALFD */
-#define signalfd_deliver(t, s) do { } while (0)
-#define signalfd_notify(t, s) do { } while (0)
-#define signalfd_detach_locked(t) do { } while (0)
-#define signalfd_detach(t) do { } while (0)
+static inline void signalfd_notify(struct task_struct *tsk, int sig) { }
#endif /* CONFIG_SIGNALFD */
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