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 <davidel@xmailserver.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 4 insertions, 15 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 06b24b3aa370..993369ee94d1 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 7332e236d367..33f12f48684a 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 3169bed0b4d0..9fb91a32edda 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){
                 /*