From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Date: Thu, 09 Sep 2010 15:14:43 +0000 Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument Message-Id: <201009091714.44013.arnd@arndb.de> List-Id: References: <1283711539-7123-1-git-send-email-segooon@gmail.com> <201009072200.59509.arnd@arndb.de> <20100907205015.GJ2448@linux.vnet.ibm.com> In-Reply-To: <20100907205015.GJ2448@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: paulmck@linux.vnet.ibm.com Cc: Kulikov Vasiliy , kernel-janitors@vger.kernel.org, Neil Brown , Jens Axboe , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org On Tuesday 07 September 2010, Paul E. McKenney wrote: > On Tue, Sep 07, 2010 at 10:00:58PM +0200, Arnd Bergmann wrote: > > On Tuesday 07 September 2010 21:21:55 Kulikov Vasiliy wrote: > > > #define __rcu_dereference_check(p, c, space) \ > > > ({ \ > > > typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ > > > ^ > > > rcu_lockdep_assert(c); \ > > > (void) (((typeof (*p) space *)p) = p); \ > > > ^ ^ > > > smp_read_barrier_depends(); \ > > > ((typeof(*p) __force __kernel *)(_________p1)); \ > > > }) > > > > > > If I understand this, it is evaluated three times, right? > > > > Yes, that looks like my own fault, I added that :( > > > > This patch seems to fix it, but I need to think about it some more > > to make sure it still does everything we need. > > Let me know when you are satisfied with it, and then I will pick it up. I guess it would be good to put it in now. I haven't had the time to try out all cases, but the current code in -next is definitely broken, so please put the fix in now. Arnd