Re: [Xenomai-core] [Xenomai-git] Jan Kiszka : nucleus: Fix race between gatekeeper and thread deletion

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

[-- Attachment #1: Type: text/plain, Size: 1320 bytes --]

On 2011-07-11 21:10, Jan Kiszka wrote:
> On 2011-07-11 20:53, Gilles Chanteperdrix wrote:
>> On 07/08/2011 06:29 PM, GIT version control wrote:
>>> @@ -2528,6 +2534,22 @@ static inline void do_taskexit_event(struct task_struct *p)
>>>  	magic = xnthread_get_magic(thread);
>>>  
>>>  	xnlock_get_irqsave(&nklock, s);
>>> +
>>> +	gksched = thread->gksched;
>>> +	if (gksched) {
>>> +		xnlock_put_irqrestore(&nklock, s);
>>
>> Are we sure irqs are on here? Are you sure that what is needed is not an
>> xnlock_clear_irqon?
> 
> We are in the context of do_exit. Not only IRQs are on, also preemption.
> And surely no nklock is held.
> 
>> Furthermore, I do not understand how we
>> "synchronize" with the gatekeeper, how is the gatekeeper garanteed to
>> wait for this assignment?
> 
> The gatekeeper holds the gksync token while it's active. We request it,
> thus we wait for the gatekeeper to become idle again. While it is idle,
> we reset the queued reference - but I just realized that this may tramp
> on other tasks' values. I need to add a check that the value to be
> null'ified is actually still ours.

Thinking again, that's actually not a problem: gktarget is only needed
while gksync is zero - but then we won't get hold of it anyway and,
thus, can't cause any damage.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 262 bytes --]