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    SubjectRe: [PATCH v2 5/7] signal: sigprocmask() should do retarget_shared_pending()
    On Mon, 18 Apr 2011 15:45:57 +0200
    Oleg Nesterov <oleg@redhat.com> wrote:

    > In short, almost every changing of current->blocked is wrong, or at least
    > can lead to the unexpected results.
    >
    > For example. Two threads T1 and T2, T1 sleeps in sigtimedwait/pause/etc.
    > kill(tgid, SIG) can pick T2 for TIF_SIGPENDING. If T2 calls sigprocmask()
    > and blocks SIG before it notices the pending signal, nobody else can handle
    > this pending shared signal.
    >
    > I am not sure this is bug, but at least this looks strange imho. T1 should
    > not sleep forever, there is a signal which should wake it up.
    >
    > This patch moves the code which actually changes ->blocked into the new
    > helper, set_current_blocked() and changes this code to call
    > retarget_shared_pending() as exit_signals() does. We should only care about
    > the signals we just blocked, we use "newset & ~current->blocked" as a mask.
    >
    > We do not check !sigisemptyset(newblocked), retarget_shared_pending() is
    > cheap unless mask & shared_pending.
    >
    > Note: for this particular case we could simply change sigprocmask() to
    > return -EINTR if signal_pending(), but then we should change other callers
    > and, more importantly, if we need this fix then set_current_blocked() will
    > have more callers and some of them can't restart. See the next patch as a
    > random example.
    >
    > Signed-off-by: Oleg Nesterov <oleg@redhat.com>

    This looks much simpler to me.

    Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com>


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