Re: sparse: possible false report of context imbalance

[Larry Finger]

On 10/17/2013 11:25 AM, Josh Triplett wrote:
> 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.

Thanks for the answer, which is about what I expected. Sparse is a great tool, 
particularly for endian-related issues.

Larry

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