Messages in this thread | | | Date | Thu, 29 Nov 2018 11:10:00 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 25/27] locking/lockdep: Add support for dynamic keys |
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On Wed, Nov 28, 2018 at 03:43:23PM -0800, Bart Van Assche wrote: > +/* hash_entry is used to keep track of dynamically allocated keys. */ > struct lock_class_key { > + struct hlist_node hash_entry; > struct lockdep_subclass_key subkeys[MAX_LOCKDEP_SUBCLASSES]; > };
One consideration; and maybe we should have a BUILD_BUG for that, is that this object should be no larger than the smallest lock primitive.
That typically is raw_spinlock_t, which normally is 4 bytes, but with lockdep on that at least also includes struct lockdep_map.
So what we want is:
sizeof(lock_class_key) <= sizeof(raw_spinlock_t)
Otherwise, two consecutive spinlocks could end up with key overlap in their subclass range.
Now, I think that is still valid after this patch, but it is something that gave me pause.
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