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    Subject[patch 06/28] signalfd: fix interaction with posix-timers
    -stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Oleg Nesterov <oleg@tv-sign.ru>

    dequeue_signal:

    if (__SI_TIMER) {
    spin_unlock(&tsk->sighand->siglock);
    do_schedule_next_timer(info);
    spin_lock(&tsk->sighand->siglock);
    }

    Unless tsk == curent, this is absolutely unsafe: nothing prevents tsk from
    exiting. If signalfd was passed to another process, do_schedule_next_timer()
    is just wrong.

    Add yet another "tsk == current" check into dequeue_signal().

    This patch fixes an oopsable bug, but breaks the scheduling of posix timers
    if the shared __SI_TIMER signal was fetched via signalfd attached to another
    sub-thread. Mostly fixed by the next patch.

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Davide Libenzi <davidel@xmailserver.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Michael Kerrisk <mtk-manpages@gmx.net>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    kernel/signal.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/kernel/signal.c
    +++ b/kernel/signal.c
    @@ -368,7 +368,7 @@ int dequeue_signal(struct task_struct *t
    /* We only dequeue private signals from ourselves, we don't let
    * signalfd steal them
    */
    - if (tsk == current)
    + if (likely(tsk == current))
    signr = __dequeue_signal(&tsk->pending, mask, info);
    if (!signr) {
    signr = __dequeue_signal(&tsk->signal->shared_pending,
    @@ -415,7 +415,7 @@ int dequeue_signal(struct task_struct *t
    if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT))
    tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
    }
    - if ( signr &&
    + if (signr && likely(tsk == current) &&
    ((info->si_code & __SI_MASK) == __SI_TIMER) &&
    info->si_sys_private){
    /*
    --
    -
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