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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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