Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b8fceee17a310f189188599a8fa5e9beaff57eb0
Commit:     b8fceee17a310f189188599a8fa5e9beaff57eb0
Parent:     9db619e66503494e41159de3c76fafabe80d016b
Author:     Davide Libenzi <[EMAIL PROTECTED]>
AuthorDate: Thu Sep 20 12:40:16 2007 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Thu Sep 20 13:19:59 2007 -0700

    signalfd simplification
    
    This simplifies signalfd code, by avoiding it to remain attached to the
    sighand during its lifetime.
    
    In this way, the signalfd remain attached to the sighand only during
    poll(2) (and select and epoll) and read(2).  This also allows to remove
    all the custom "tsk == current" checks in kernel/signal.c, since
    dequeue_signal() will only be called by "current".
    
    I think this is also what Ben was suggesting time ago.
    
    The external effect of this, is that a thread can extract only its own
    private signals and the group ones.  I think this is an acceptable
    behaviour, in that those are the signals the thread would be able to
    fetch w/out signalfd.
    
    Signed-off-by: Davide Libenzi <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 fs/exec.c                 |    3 -
 fs/signalfd.c             |  190 +++++++--------------------------------------
 include/linux/init_task.h |    2 +-
 include/linux/sched.h     |    2 +-
 include/linux/signalfd.h  |   40 +---------
 kernel/exit.c             |    9 --
 kernel/fork.c             |    2 +-
 kernel/signal.c           |    8 +-
 8 files changed, 39 insertions(+), 217 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index c21a8cc..073b0b8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -50,7 +50,6 @@
 #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>
@@ -784,7 +783,6 @@ static int de_thread(struct task_struct *tsk)
         * and we can just re-use it all.
         */
        if (atomic_read(&oldsighand->count) <= 1) {
-               signalfd_detach(tsk);
                exit_itimers(sig);
                return 0;
        }
@@ -923,7 +921,6 @@ static int de_thread(struct task_struct *tsk)
        sig->flags = 0;
 
 no_thread_group:
-       signalfd_detach(tsk);
        exit_itimers(sig);
        if (leader)
                release_task(leader);
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 <[EMAIL PROTECTED]>
+ *  Sat May 19, 2007: Davi E. M. Arnaut <[EMAIL PROTECTED]>
  *      Retrieve multiple signals with one read() call
+ *  Sun Jul 15, 2007: Davide Libenzi <[EMAIL PROTECTED]>
+ *      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;
 }
 
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index cab741c..f8abfa3 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -86,7 +86,7 @@ extern struct nsproxy init_nsproxy;
        .count          = ATOMIC_INIT(1),                               \
        .action         = { { { .sa_handler = NULL, } }, },             \
        .siglock        = __SPIN_LOCK_UNLOCKED(sighand.siglock),        \
-       .signalfd_list  = LIST_HEAD_INIT(sighand.signalfd_list),        \
+       .signalfd_wqh   = __WAIT_QUEUE_HEAD_INITIALIZER(sighand.signalfd_wqh),  
\
 }
 
 extern struct group_info init_groups;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3de7901..a01ac6d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -438,7 +438,7 @@ struct sighand_struct {
        atomic_t                count;
        struct k_sigaction      action[_NSIG];
        spinlock_t              siglock;
-       struct list_head        signalfd_list;
+       wait_queue_head_t       signalfd_wqh;
 };
 
 struct pacct_struct {
diff --git a/include/linux/signalfd.h b/include/linux/signalfd.h
index 5104294..4c9ff09 100644
--- a/include/linux/signalfd.h
+++ b/include/linux/signalfd.h
@@ -45,49 +45,17 @@ struct signalfd_siginfo {
 #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 */
 
diff --git a/kernel/exit.c b/kernel/exit.c
index 06b24b3..993369e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -24,7 +24,6 @@
 #include <linux/pid_namespace.h>
 #include <linux/ptrace.h>
 #include <linux/profile.h>
-#include <linux/signalfd.h>
 #include <linux/mount.h>
 #include <linux/proc_fs.h>
 #include <linux/kthread.h>
@@ -86,14 +85,6 @@ static void __exit_signal(struct task_struct *tsk)
        sighand = rcu_dereference(tsk->sighand);
        spin_lock(&sighand->siglock);
 
-       /*
-        * Notify that this sighand has been detached. This must
-        * be called with the tsk->sighand lock held. Also, this
-        * access tsk->sighand internally, so it must be called
-        * before tsk->sighand is reset.
-        */
-       signalfd_detach_locked(tsk);
-
        posix_cpu_timers_exit(tsk);
        if (atomic_dec_and_test(&sig->count))
                posix_cpu_timers_exit_group(tsk);
diff --git a/kernel/fork.c b/kernel/fork.c
index 7332e23..33f12f4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1438,7 +1438,7 @@ static void sighand_ctor(void *data, struct kmem_cache 
*cachep,
        struct sighand_struct *sighand = data;
 
        spin_lock_init(&sighand->siglock);
-       INIT_LIST_HEAD(&sighand->signalfd_list);
+       init_waitqueue_head(&sighand->signalfd_wqh);
 }
 
 void __init proc_caches_init(void)
diff --git a/kernel/signal.c b/kernel/signal.c
index 3169bed..9fb91a3 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -378,8 +378,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, 
siginfo_t *info)
        /* We only dequeue private signals from ourselves, we don't let
         * signalfd steal them
         */
-       if (likely(tsk == current))
-               signr = __dequeue_signal(&tsk->pending, mask, info);
+       signr = __dequeue_signal(&tsk->pending, mask, info);
        if (!signr) {
                signr = __dequeue_signal(&tsk->signal->shared_pending,
                                         mask, info);
@@ -407,8 +406,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, 
siginfo_t *info)
                        }
                }
        }
-       if (likely(tsk == current))
-               recalc_sigpending();
+       recalc_sigpending();
        if (signr && unlikely(sig_kernel_stop(signr))) {
                /*
                 * Set a marker that we have dequeued a stop signal.  Our
@@ -425,7 +423,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, 
siginfo_t *info)
                if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT))
                        tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
        }
-       if (signr && likely(tsk == current) &&
+       if (signr &&
             ((info->si_code & __SI_MASK) == __SI_TIMER) &&
             info->si_sys_private){
                /*
-
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