On Thu, Apr 12, 2007 at 07:52:20AM +0530, Srivatsa Vaddagiri wrote:
> I wonder if there is some value in "enforcing" an order in which
> processes get frozen i.e freeze A first before B. That may solve the
> deadlocks we have been discussing wrt kthread_stop and flush_workqueue
> as well.
>
> The idea is similar to how deadlock wrt multiple locks are solved -
> where a ordering is enforced. Take Lock A first before Lock B.
>
> If process A waits on B (like in kthread_stop or flush_workqueue), then if we:
>
> 1. Insert A and B in a list (freeze_me_first_list)
In that case, A should insert the dependency into the
freeze_me_first_list as B is unaware of the dependency yet.
What if by the time A has inserted the dependency B is already frozen?
Can very well happen right?
A: B: freezer
-------------------------------------------------------------------------------
*Check the list. don't find A/B
*Mark A freezeable.
*Mark B freezeable.
*try_to_freeze();
*insert A, B .
into the .
list. .
.
.
* wait_for_ .
completion(done); . /* Freezer fails at this
. * point
. */
.
.
*complete(done);
*try_to_freeze();
Example: A = a thread doing flush_workqueue.
B = worker thread.
Of course, we can always use the freezer_skip around this
wait_for_completion as well as long as the thread A is not marked
PF_NOFREEZE. But with multiple freeze events, it won't be as simple as
that.
> --
> Regards,
> vatsa
Thanks and Regards
gautham.
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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