Re: [Xenomai-core] x86: Endless minor faults

[Jan Kiszka <jan.kiszka@domain.hid>]

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Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> On archs with non-atomic switch_mm(), use_mm() will require a different
>> strategy. I'm thinking about something like
>>
>> use_mm():
>> 	set_some_flag();
>> 	barrier();
>> 	current->mm = new_mm;
>> 	current->active_mm = new_mm;
>> 	switch_mm(old_active_mm, new_mm, current);
>> 	clear_some_flag();
>>
>> and switch_mm():
>> 	...
>> 	if (likely(prev != next) || some_flag_set()) {
>> 		clear_some_flag();
>> 		...
>>
>> ie. enforce mm switch if we may have interrupted use_mm at an unpleasant
>> time. I just don't know yet where to attach that some_flag to. Should be
>> the current task, but can we always access it from switch_mm?
> 
> These mechanisms are already in place. All you have to do is:
> 
> use_mm()
> 	ipipe_active_mm = NULL;
> 	barrier();
> 	current->mm = new_mm;
> 	current->active_mm = new_mm;
> 	switch_mm(old_active_mm, new_mm, current);
> 

As far as I understand, ipipe_active_mm has different semantics on ARM.
Specifically, it has no relation to the initial "next != prev" check.
The test we need is likely orthogonal to this.

Jan


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