Fatal exceptions on context-switching for more than two isolated threads
utkarsh.rai60 at gmail.com
Tue Sep 22 14:58:50 UTC 2020
On Mon, Sep 21, 2020 at 10:29 PM Gedare Bloom <gedare at rtems.org> wrote:
> On Sat, Sep 19, 2020 at 5:41 AM Utkarsh Rai <utkarsh.rai60 at gmail.com>
> > Hello,
> > When I isolate more than two threads in RTEMS (the implementation can be
> found here), I get fatal exceptions while context-switching. On stepping
> into the code, the problem seems to be with the _User_extensions_Thread_*()
> call just after a context-switch, in particular when the iterators are
> initialized inside this call. The issue is the fact that we mark the stack
> space of the switched out thread as 'NO_ACESS' and then try to access
> iterators(which belong to the stack space of the switched-out thread) from
> a different thread, which leads to fatal exceptions.
> > I am not sure how to handle this issue because I am not very clear on
> the purpose of the "user extension" functionality or its implementation.
> Any help would be appreciated, as this may possibly be the last hurdle for
> a mergeable thread stack isolation feature.
> Are you testing in an SMP configuration? The user extensions in
> uniprocessor run before the context switch.
No, I am running with a simple uniprocessor configuration.
> It would help if you
> provide a trace of your debug.
The backtrace -
_Chain_Append_unprotected (the_chain=0x2002a0 <_User_extensions_List+12>,
#1 0x0010d630 in _Chain_Iterator_initialize (
#2 0x0010d92e in _User_extensions_Iterate (
#3 0x0010a172 in _User_extensions_Thread_begin (
#4 0x0010a21c in _Thread_Handler ()
#5 0x0010e1e8 in _CPU_Context_switch_arm ()
The previous node of the chain was at 0xfbf7a0 which has been
You might consider using the event
> recorder to also help with your debugging.
Ok, I will look into it.
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