Messages in this thread | | | Subject | Re: [RFC][PATCH 9/7] mm: fix mm_take_all_locks() locking order | From | Peter Zijlstra <> | Date | Fri, 08 Aug 2008 09:16:15 +0200 |
| |
On Thu, 2008-08-07 at 23:46 +0200, Andrea Arcangeli wrote:
> As for 8/7 you know my opinion from somebody who's way beyond the > point: check_deadlock should be dropped
I'll try again one more time, don't feel obliged to reply or anything :-)
Suppose you have objects initialized from a single site:
struct my_obj *create_obj() { ... spin_lock_init(&obj->lock); ...
return obj; }
So that all these object's their locks are in a single class.
Now, put these objects into two lists without fixed order.
L1: A B C D L2: B A D C
If you were to lock-couple your way through these lists there is a deadlock potential.
The check_noncircular stuff will not catch this due to it all being of a single class. The only thing we have to indicate you need to pay attention is check_deadlock.
Yes, check_deadlock is a tad too sensitive in the amount of false positives, but without it there are gaping holes in 'proving' lock correctness.
Currently - if you get 100% code coverage and lockdep doesn't shout, you're good. If we were to drop check_deadlock we can't say that anymore.
| |