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Subject[PATCH 8/6] signals: send_signal: factor out SIGNAL_GROUP_EXIT checks
The signal has no effect (but can provoke the unnecessary wakeup) if the
thread group is dying. Let's make this explicit and check SIGNAL_GROUP_EXIT
only once in handle_stop_signal() renamed to prepare_signal().

From now the actual signal-delivery path doesn't need to take the special
SIGNAL_GROUP_EXIT case into account.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 25/kernel/signal.c~8_SS_CK_SGE 2008-03-09 20:21:02.000000000 +0300
+++ 25/kernel/signal.c 2008-03-09 21:18:19.000000000 +0300
@@ -564,16 +564,16 @@ static void do_notify_parent_cldstop(str
* actual continuing for SIGCONT, but not the actual stopping for stop
* signals. The process stop is done as a signal action for SIG_DFL.
*/
-static void handle_stop_signal(int sig, struct task_struct *p)
+static int prepare_signal(int sig, struct task_struct *p)
{
struct signal_struct *signal = p->signal;
struct task_struct *t;

- if (signal->flags & SIGNAL_GROUP_EXIT)
+ if (unlikely(signal->flags & SIGNAL_GROUP_EXIT))
/*
* The process is in the middle of dying already.
*/
- return;
+ return 0;

if (sig_kernel_stop(sig)) {
/*
@@ -644,6 +644,8 @@ static void handle_stop_signal(int sig,
signal->flags &= ~SIGNAL_STOP_DEQUEUED;
}
}
+
+ return 1;
}

/*
@@ -708,8 +710,7 @@ static void complete_signal(int sig, str
* Found a killable thread. If the signal will be fatal,
* then start taking the whole group down immediately.
*/
- if (sig_fatal(p, sig) && !(signal->flags & SIGNAL_GROUP_EXIT) &&
- !sigismember(&t->real_blocked, sig) &&
+ if (sig_fatal(p, sig) && !sigismember(&t->real_blocked, sig) &&
(sig == SIGKILL || !(t->ptrace & PT_PTRACED))) {
/*
* This signal will be fatal to the whole group.
@@ -753,7 +754,8 @@ static int send_signal(int sig, struct s
struct sigqueue *q;

assert_spin_locked(&t->sighand->siglock);
- handle_stop_signal(sig, t);
+ if (!likely(prepare_signal(sig, t)))
+ return 0;

pending = group ? &t->signal->shared_pending : &t->pending;
/*
@@ -1247,9 +1249,10 @@ int send_sigqueue(struct sigqueue *q, st
if (!likely(lock_task_sighand(t, &flags)))
goto ret;

- handle_stop_signal(sig, t);
-
ret = 1;
+ if (!likely(prepare_signal(sig, t)))
+ goto out;
+
if (sig_ignored(t, sig))
goto out;



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