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SubjectRe: [PATCH v2 21/24] locking/lockdep: Verify whether lock objects are small enough to be used as class keys
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On 12/03/2018 07:28 PM, Bart Van Assche wrote:
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Johannes Berg <johannes@sipsolutions.net>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
> kernel/locking/lockdep.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index c936fce5b9d7..b4772e5fc176 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -727,6 +727,15 @@ static bool assign_lock_key(struct lockdep_map *lock)
> {
> unsigned long can_addr, addr = (unsigned long)lock;
>
> + /*
> + * lockdep_free_key_range() assumes that struct lock_class_key
> + * objects do not overlap. Since we use the address of lock
> + * objects as class key for static objects, check whether the
> + * size of lock_class_key objects does not exceed the size of
> + * the smallest lock object.
> + */
> + BUILD_BUG_ON(sizeof(struct lock_class_key) > sizeof(raw_spinlock_t));
> +
> if (__is_kernel_percpu_address(addr, &can_addr))
> lock->key = (void *)can_addr;
> else if (__is_module_percpu_address(addr, &can_addr))

I don't understand what this check is for. lock_class_key and spinlock
are different objects. Their relative size shouldn't matter.

Cheers,
Longman

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