On 2012-10-10 11:23, Gilles Chanteperdrix wrote: > On 10/10/2012 11:01 AM, Jan Kiszka wrote: >> On 2012-10-10 10:58, Gilles Chanteperdrix wrote: >>> On 10/10/2012 10:10 AM, Jan Kiszka wrote: >>>> On 2012-10-10 10:04, Gilles Chanteperdrix wrote: >>>>> On 10/10/2012 09:56 AM, Jan Kiszka wrote: >>>>>> On 2012-10-10 09:51, Gilles Chanteperdrix wrote: >>>>>>> On 10/10/2012 09:38 AM, Thierry Bultel wrote: >>>>>>>> Hi Gilles, >>>>>>>> >>>>>>>> Many thanks, >>>>>>>> The first patch does not work, the second does. >>>>>>>> I think the reason for 1st patch why is that in rtcan_virt, we have >>>>>>>> >>>>>>>> rtdm_lock_get_irqsave(&rtcan_recv_list_lock, lock_ctx); >>>>>>>> rtdm_lock_get(&rtcan_socket_lock); >>>>>>>> >>>>>>>> ... >>>>>>>> ---> rtcan_rcv(rx_dev, &skb); >>>>>>>> .... >>>>>>>> >>>>>>>> rtdm_lock_put(&rtcan_socket_lock); >>>>>>>> rtdm_lock_put_irqrestore(&rtcan_recv_list_lock, lock_ctx); >>>>>>>> >>>>>>>> and rtcan_rcv->rtcan_rcv_deliver->rtdm_sem_up(&sock->recv_sem); >>>>>>>> >>>>>>>> thus the same re-scheduling stuff with interrupts locked. >>>>>>>> >>>>>>>> Are you not not afraid of side effects with the second patch, >>>>>>>> since you change the overall behaviour ? >>>>>>>> Won't you prefer a only locally modified rtcan_virt ? >>>>>>> >>>>>>> We should ask Jan's opinion. In any case, if we adopt the second patch, >>>>>>> we might want to try and reduce the overhead of xnpod_unlock_sched. >>>>>>> >>>>>> >>>>>> We were signaling the semaphore while holding a spin lock? That's a >>>>>> clear bug. Your patch is aligning rtcan to the pattern we are also using >>>>>> in RTnet. We just need to make sure (haven't looked at the full context >>>>>> yet) that sock remains valid even after dropping the lock(s). >>>>> >>>>> The second patch idea was to lock the scheduler while spinlocks are >>>>> held, so that posting a semaphore while holding a spin lock is no longer >>>>> a bug. >>>> >>>> Sounds a bit hacky, >>> >>> Well, that is what the linux kernel does. >>> >>> but I think we have this pattern >>>> (RTDM_EXECUTE_ATOMICALLY) >>> >>> RTDM_EXECUTE_ATOMICALLY is a bit of a misnomer, if you do: >>> RTDM_EXECUTE_ATOMICALLY(foo(); rtdm_sem_up(); bar()); >>> foo() and bar() are not executed atomically if sem_up wakes up another >>> thread. >>> >>> So, I do not see how RTDM_EXECUTE_ATOMICALLY solves the issue we are >>> talking about. >> >> RTDM_EXECUTE_ATOMICALLY holds the nucleus lock across the encapsulated >> code, executing it atomically as rescheduling is postponed until the end >> of the block. > > Err... no. Absolutely not.
Err... absolutely right. The good news is: we don't need to worry about such kind of locking. In rtcan_raw_recvmsg, the socket is locked via the RTDM context as we are in a handler. So it won't disappear when we drop the lock, and your first patch is fine. Jan -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 259 bytes Desc: OpenPGP digital signature URL: <http://www.xenomai.org/pipermail/xenomai/attachments/20121010/baf3ed37/attachment.pgp> _______________________________________________ Xenomai mailing list [email protected] http://www.xenomai.org/mailman/listinfo/xenomai
