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    Subject[PATCH v2 3/6] signal: do_sigtimedwait() needs retarget_shared_pending()
    do_sigtimedwait() changes current->blocked and thus it needs
    set_current_blocked()->retarget_shared_pending().

    We could use set_current_blocked() directly. It is fine to change
    ->real_blocked from all-zeroes to ->blocked and vice versa lockless,
    but this is not immediately clear, looks racy, and needs a huge
    comment to explain why this is correct.

    To keep the things simple this patch adds the new static helper,
    __set_task_blocked() which should be called with ->siglock held. This
    way we can change both ->real_blocked and ->blocked atomically under
    ->siglock as the current code does. This is more understandable.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Tejun Heo <tj@kernel.org>
    Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com>
    ---

    kernel/signal.c | 21 +++++++++++++--------
    1 file changed, 13 insertions(+), 8 deletions(-)

    --- sigprocmask/kernel/signal.c~3_sigtimedwait_retarget 2011-04-26 19:53:42.000000000 +0200
    +++ sigprocmask/kernel/signal.c 2011-04-26 19:53:55.000000000 +0200
    @@ -2115,11 +2115,8 @@ long do_no_restart_syscall(struct restar
    return -EINTR;
    }

    -void set_current_blocked(const sigset_t *newset)
    +static void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset)
    {
    - struct task_struct *tsk = current;
    -
    - spin_lock_irq(&tsk->sighand->siglock);
    if (signal_pending(tsk) && !thread_group_empty(tsk)) {
    sigset_t newblocked;
    signandsets(&newblocked, newset, &current->blocked);
    @@ -2127,6 +2124,14 @@ void set_current_blocked(const sigset_t
    }
    tsk->blocked = *newset;
    recalc_sigpending();
    +}
    +
    +void set_current_blocked(const sigset_t *newset)
    +{
    + struct task_struct *tsk = current;
    +
    + spin_lock_irq(&tsk->sighand->siglock);
    + __set_task_blocked(tsk, newset);
    spin_unlock_irq(&tsk->sighand->siglock);
    }

    @@ -2343,7 +2348,8 @@ int do_sigtimedwait(const sigset_t *whic
    /*
    * None ready, temporarily unblock those we're interested
    * while we are sleeping in so that we'll be awakened when
    - * they arrive.
    + * they arrive. Unblocking is always fine, we can avoid
    + * set_current_blocked().
    */
    tsk->real_blocked = tsk->blocked;
    sigandsets(&tsk->blocked, &tsk->blocked, &mask);
    @@ -2353,10 +2359,9 @@ int do_sigtimedwait(const sigset_t *whic
    timeout = schedule_timeout_interruptible(timeout);

    spin_lock_irq(&tsk->sighand->siglock);
    - sig = dequeue_signal(tsk, &mask, info);
    - tsk->blocked = tsk->real_blocked;
    + __set_task_blocked(tsk, &tsk->real_blocked);
    siginitset(&tsk->real_blocked, 0);
    - recalc_sigpending();
    + sig = dequeue_signal(tsk, &mask, info);
    }
    spin_unlock_irq(&tsk->sighand->siglock);



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