[PATCH 7/6] signals: handle_stop_signal: don't worry about SIGKILL - Kernel

This is a discussion on [PATCH 7/6] signals: handle_stop_signal: don't worry about SIGKILL - Kernel ; handle_stop_signal() clears SIGNAL_STOP_DEQUEUED when sig == SIGKILL. Remove this nasty special case. It was needed to prevent the race with group stop and exit caused by thread-specific SIGKILL. Now that we use complete_signal() for private signals too this is not ...

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Thread: [PATCH 7/6] signals: handle_stop_signal: don't worry about SIGKILL

  1. [PATCH 7/6] signals: handle_stop_signal: don't worry about SIGKILL

    handle_stop_signal() clears SIGNAL_STOP_DEQUEUED when sig == SIGKILL. Remove
    this nasty special case. It was needed to prevent the race with group stop and
    exit caused by thread-specific SIGKILL. Now that we use complete_signal() for
    private signals too this is not needed, complete_signal() will notice SIGKILL
    and abort the soon-to-begin group stop.

    Except: the target thread is dead (has PF_EXITING). But in that case we should
    not just clear SIGNAL_STOP_DEQUEUED and nothing more. We should either kill
    the whole thread group, or silently ignore the signal.

    I suspect we are not right wrt zombie leaders, but this is another issue which
    and should be fixed separately. Note that this check can't abort the group stop
    if it was already started/finished, this check only adds a subtle side effect
    if we race with the thread which has already dequeued sig_kernel_stop() signal
    and temporary released ->siglock.

    Signed-off-by: Oleg Nesterov

    --- 25/kernel/signal.c~7_HSS_NO_KILL 2008-03-09 17:48:28.000000000 +0300
    +++ 25/kernel/signal.c 2008-03-09 20:21:02.000000000 +0300
    @@ -643,12 +643,6 @@ static void handle_stop_signal(int sig,
    */
    signal->flags &= ~SIGNAL_STOP_DEQUEUED;
    }
    - } else if (sig == SIGKILL) {
    - /*
    - * Make sure that any pending stop signal already dequeued
    - * is undone by the wakeup for SIGKILL.
    - */
    - signal->flags &= ~SIGNAL_STOP_DEQUEUED;
    }
    }


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  2. Re: [PATCH 7/6] signals: handle_stop_signal: don't worry about SIGKILL

    This look OK to me too. I'm not 100% sure we didn't overlook some subtlety.
    But I think your analysis is sound.


    Thanks,
    Roland
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