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    Subject[PATCH 17/23] tracehook: force signal_pending()
    Date
    This defines a new hook tracehook_force_sigpending() that lets
    tracing code decide to force TIF_SIGPENDING on in recalc_sigpending().

    This is not used yet, so it compiles away to nothing for now.
    It lays the groundwork for new tracing code that can interrupt
    a task synthetically without actually sending a signal.

    Signed-off-by: Roland McGrath <roland@redhat.com>
    ---
    include/linux/tracehook.h | 14 ++++++++++++++
    kernel/signal.c | 4 +++-
    2 files changed, 17 insertions(+), 1 deletions(-)

    diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
    index 4c50e1b..43bc51b 100644
    --- a/include/linux/tracehook.h
    +++ b/include/linux/tracehook.h
    @@ -423,6 +423,20 @@ static inline int tracehook_consider_fatal_signal(struct task_struct *task,
    }

    /**
    + * tracehook_force_sigpending - let tracing force signal_pending(current) on
    + *
    + * Called when recomputing our signal_pending() flag. Return nonzero
    + * to force the signal_pending() flag on, so that tracehook_get_signal()
    + * will be called before the next return to user mode.
    + *
    + * Called with @current->sighand->siglock held.
    + */
    +static inline int tracehook_force_sigpending(void)
    +{
    + return 0;
    +}
    +
    +/**
    * tracehook_get_signal - deliver synthetic signal to traced task
    * @task: @current
    * @regs: task_pt_regs(@current)
    diff --git a/kernel/signal.c b/kernel/signal.c
    index cbec18e..44b5823 100644
    --- a/kernel/signal.c
    +++ b/kernel/signal.c
    @@ -134,7 +134,9 @@ void recalc_sigpending_and_wake(struct task_struct *t)

    void recalc_sigpending(void)
    {
    - if (!recalc_sigpending_tsk(current) && !freezing(current))
    + if (unlikely(tracehook_force_sigpending()))
    + set_thread_flag(TIF_SIGPENDING);
    + else if (!recalc_sigpending_tsk(current) && !freezing(current))
    clear_thread_flag(TIF_SIGPENDING);

    }

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