On Fri, 10 Apr 2015, Sebastian Andrzej Siewior wrote:
> >And: please test it, too. (patch the kernel so that you can trigger
> >this case).
>
> Why patch? Isn't this triggered if you have a reader waiting and you
> send a message?
Manfred referred to the exit race. Though you can spare that exercise
as it is safe by definition if you hold a ref on the task.
Can you please convert that over to Peters lockless wake queues so we
do not reimplement the same thing open coded here.
> +static struct task_struct *pipelined_send(struct mqueue_inode_info *info,
> struct msg_msg *message,
> struct ext_wait_queue *receiver)
> {
> + struct task_struct *r_task;
> +
> receiver->msg = message;
> list_del(&receiver->list);
> - receiver->state = STATE_PENDING;
> - wake_up_process(receiver->task);
> + r_task = receiver->task;
> + get_task_struct(r_task);
> smp_wmb();
While we are at it. The barrier here and the one in pipelined_receive
are not documented and they are missing a proper pairing on the read
side. The comment which you removed was pretty vague about the purpose
of the barrier as well.
Thanks,
tglx
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