On Thu, 7 Aug 2014 17:17:41 +0200
Peter Zijlstra <pet...@infradead.org> wrote:
> Subject: atm: Fix blocking in wait loop
>
> One should not call blocking primitives inside a wait loop, since both
> require task_struct::state to sleep, so the inner will destroy the outer
> state.
>
> In this instance sigd_enq() will possible sleep for alloc_skb(), now if
> I understand the code right, we do not actually need to call sigd_enq()
> after the initial prepare_to_wait(), because we test the termination
> condition before schedule() anyhow.
>
> So we can simply move it up a bit and avoid the entire confusion.
>
> Signed-off-by: Peter Zijlstra <pet...@infradead.org>
> ---
> net/atm/svc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/atm/svc.c b/net/atm/svc.c
> index d8e5d0c2ebbc..445ac238b69b 100644
> --- a/net/atm/svc.c
> +++ b/net/atm/svc.c
> @@ -297,8 +297,8 @@ static int svc_listen(struct socket *sock, int backlog)
> goto out;
> }
> set_bit(ATM_VF_WAITING, &vcc->flags);
> - prepare_to_wait(sk_sleep(sk), &wait, TASK_UNINTERRUPTIBLE);
> sigd_enq(vcc, as_listen, NULL, NULL, &vcc->local);
> + prepare_to_wait(sk_sleep(sk), &wait, TASK_UNINTERRUPTIBLE);
> while (test_bit(ATM_VF_WAITING, &vcc->flags) && sigd) {
> schedule();
> prepare_to_wait(sk_sleep(sk), &wait, TASK_UNINTERRUPTIBLE);
This isn't the only place that we queue a message for the signalling
daemon after a prepare_to_wait() uninterruptibly so this patch would
be incomplete as is.
What bothers me is the TASK_UNINTERRUPTIBLE -- I don't have a good
reason why any of these should be sleeping uninterruptibly.
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