ex_regs system call is forzed in the do_ipc process

Guanghui, Cheng cheng.guanghui.ml at gmail.com
Wed Oct 21 09:25:51 CEST 2009

On Wednesday 21 October 2009 00:44:34 Adam Lackorzynski wrote:
> Hi,
> On Tue Oct 20, 2009 at 16:20:03 +0800, Guanghui, Cheng wrote:
> > 	When i use the ex_regs system call to trigger the exception ipc
> > it seems to be frozed in the do_ipc stange. I use jdb to debug this
> > current thread lists is like this:
> >
> > 9.04 l4ertl.exceptio    10   9.03           rcv,ipc_progr
> > 9.03 l4ertl.timer0       10   9.02           rcv,ipc_progr
> > 9.02 domain2.main   10    9.04       rcv,ipc_progr,exc_progr
> >
> > 	l4ertl.exceptio is the pager of domain2.main. And now l4ertl.timer0
> > is executing ex_regs system to trigger exception for domain2.main.
> > l4ertl.exceptio is waiting for the exception ipc from the l4ertl2.main2.
> > 	In detail l4ertl.exceptio is in ipc (user level registers).
> > l4ertl.timer0 is in ipc (user level registers), too. domain2.main is in
> > the exception 255. It seems to be dead lock in the kernel.  Very strange.
> I think that's what the L4_THREAD_EX_REGS_NO_CANCEL flag is about.
> 'cancel' here means that a possibly ongoing IPC is being canceled, i.e.
> aborted. When you remove the flag, the IPCs will be aborted and return.
	It can't work either. I tested my demo many times and found:
If the thread in which the exception ipc will be triggered is only 1 L4 thread 
or is 1 L4eRTL thread (You know in my design there are many L4eRTL threads in 
the L4 main thread), the exception ipc could be triggered correctly. But i 
don't test two l4ertl threads because only one can't work.
	If i ajust the exception handler when the L4 thread is runnning in the L4 
thread but i try to trigger the exception ipc when the main thread is running 
in the L4eRTL thread, the ex_regs system call can't return and it seems it 
will be blocked in the kernel whatever i used "L4_THREAD_EX_REGS_NO_CANCEL" 
or not. Vice versa.
							Cheng Guanghui

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