On Mon, Nov 30, 2009 at 15:20, Peter Soetens <pe...@thesourceworks.com> wrote:
> On Thu, Nov 5, 2009 at 02:46, Gilles Chanteperdrix
> <gilles.chanteperd...@xenomai.org> wrote:
>>
>> Peter Soetens wrote:
>> > Hi,
>> >
>> > I'm creating my RT threads using the native API and I'm creating
>> > mqueues, wrapped to the pthread_rt library.
>> > I can read and write the mqueue (and it goes through Xenomai), but
>> > when I select() on a receiving mqd_t, the select() calls returns that
>> > there is data available on the mq (it fills in the FD_SET), but keeps
>> > doing so even when it's empty (the select() is in a loop). Also, it's
>> > modeswitching like nuts.
>> >
>> > I found out that the __wrap_select is correctly called, but returns
>> > -EPERM. Kernel sources indicate that this is caused by
>> > pse51_current_thread() alias thread2pthread() returning null. Since
>> > EPERM is returned to userspace, the __real_select is called from user
>> > space, causing the mode switches and bad behaviour. This is almost
>> > certainly the thing that native + RTDM + select() is seeing too.
>> >
>> > My mqueues-only work probably because mq.c only uses
>> > pse51_current_thread() in the mq_notify function. I'm guessing that
>> > mq_notify would also not work in combination with native skin.
>> >
>> > I had two options in fixing this: add a xnselector to the native task
>> > struct or to the nucleus xnthread_t. I choose the latter, such that
>> > every skin kan use select() + RTDM and migrate gradualy to the RTDM
>> > and/or Posix skin.
>> > I needed to free the xnselector structure in xnpod_delete_thread() , I
>> > chose a spot, but it causes a segfault in my native thread (which did
>> > the select) during program cleanup. Any advice ? Also, maybe we should
>> > separate select() from the posix skin and put it in a separate place
>> > (in RTDM as rtdm_select() ?), such that we can start building around
>> > it (posix just forwards to rtdm_select() then).
>> >
>> > A second patch was necessary to return the timeout case properly to
>> > userspace (independent of first patch).
>> >
>> > Tested with native + posix loaded and mq. If you never quit your
>> > application, this works :-)
>>
>> Hi,
>>
>> I have included a lightly modified version of this patch on head, I do
>> not see any crash.  However, I have some doubts about the current
>> implementation: calling xnselector_destroy() opens opportunities for a
>> rescheduling, which I am not sure is really what we want in the middle
>> of xnpod_delete_thread(). Philippe, what do you think?
>
> I'll test this patch this week too. It seems you forgot to apply the
> second patch, which can go straight into the 2.4 head, since it fixes
> a bug in the select() wrapping code when timeouts are used. See
> parent's 0002-posix-Fix-__wrap_select-when-timeout-happens.patch

I tested the 2.5 branch with this patch and it works here too.

Peter

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