From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Triplett Subject: Re: sparse: possible false report of context imbalance Date: Thu, 17 Oct 2013 09:25:52 -0700 Message-ID: <20131017162551.GA4123@jtriplet-mobl1> References: <525F584C.5010106@lwfinger.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <525F584C.5010106@lwfinger.net> Sender: linux-kernel-owner@vger.kernel.org To: Larry Finger Cc: Christopher Li , Linux-Sparse , LKML List-Id: linux-sparse@vger.kernel.org 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