Re: Kernel KAPI and instrumentation mods

[Jonathan Larmour <jifl at eCosCentric dot com>]

Nick Garnett wrote:
> Jonathan Larmour <jifl@eCosCentric.com> writes:
>
>
> > Hi Nick,
> >
> > I was looking over the patch while going through the backlog and was
> > wondering about the following function. While the scheduler is locked
> > inside the function, it obviously may well not be outside. In that
> > case the thread being pointed to by current may have exitted and the
> > memory (at least partially) reused since the last invocation of
> > cyg_thread_get_next(). For example the unique id in the thread
> > structure could be intact, but the list pointers scribbled on.
>
> Well, I also added an assignment in the thread destructor to zero the
> thread id. So if the memory has been reused, even for another thread,
> the id check will fail and it won't touch the list links.
True. It makes the probability 0.001% rather than 1%. Hmm.. is this good 
enough still though. Anyone else's opinion before I potentially flog a 
dead horse?

Although I should probably throw in some CYG_CHECK_DATA_PTRs at least, but 
that won't catch anything in the field.

> > > +cyg_bool_t cyg_thread_get_info( cyg_handle_t threadh,
> > > +                                cyg_uint16 id,
> > > +                                cyg_thread_info *info )
> > > +{
> > > +    cyg_bool_t result = true;
> > > +    Cyg_Thread *thread = (Cyg_Thread *)threadh;
> > > +    +    Cyg_Scheduler::lock();
> > > +    +    if( thread->get_unique_id() == id && info != NULL )
> > > +    {
> > Why pass in the id at all if it must match the thread handle?
>
> For the same reason as above. The thread object memory may have been
> reused in the interim. Double checking the id give us a simple
> integrity check. 
Ah, I was assuming the user would be forced to use a valid thread handle 
since they "have the threads", but if they used cyg_thread_get_next i.e. 
they don't know what thread it really is, then I guess not.

Jifl
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