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SubjectRe: sparse: possible false report of context imbalance
On Wed, Oct 16, 2013 at 10:23:56PM -0500, Larry Finger wrote:
> Sparse reports the following:
>
> CHECK drivers/staging/rtl8188eu/core/rtw_mlme.c
> drivers/staging/rtl8188eu/core/rtw_mlme.c:1003:9: warning: context
> imbalance in 'rtw_free_assoc_resources' - different lock contexts
> for basic block
>
> The code in question is as follows:
>
> if (lock_scanned_queue)
> spin_lock_bh(&(pmlmepriv->scanned_queue.lock));
>
> pwlan = rtw_find_network(&pmlmepriv->scanned_queue,
> tgt_network->network.MacAddress);
>
> if (lock_scanned_queue)
> spin_unlock_bh(&(pmlmepriv->scanned_queue.lock));
>
> As this fragment uses the identical test to unlock that is used to
> lock, and the test variable is not touched, I think this is a false
> indication. I am using version 0.4.4 of sparse.

Sparse can't track conditional contexts like this; sparse intentionally
complains here that you're running the same basic block (the
rtw_find_network call) with and without a lock held.

The following workaround works when this is legitimate, though it isn't
ideal:

if (condition) {
lock
do_thing
unlock
} else {
do_thing
}

Ideally, Sparse should be able to track conditional contexts, but that
would require some form of abstract evaluation, or as a simplistic hack,
looking for identical side-effect-free conditional expressions.

- Josh Triplett


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