Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932336Ab1FGSeV (ORCPT ); Tue, 7 Jun 2011 14:34:21 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:55781 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932311Ab1FGSeU (ORCPT ); Tue, 7 Jun 2011 14:34:20 -0400 Date: Tue, 7 Jun 2011 11:34:14 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: Milton Miller , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , LKML Subject: Re: [1/4] rcu: Detect uses of rcu read side in extended quiescent states Message-ID: <20110607183414.GF2286@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1307329858-14999-3-git-send-email-fweisbec@gmail.com> <20110606181021.GL3066@linux.vnet.ibm.com> <20110607001905.GE17026@somewhere.redhat.com> <20110607004250.GZ3066@linux.vnet.ibm.com> <20110607013630.GF17026@somewhere.redhat.com> <20110607044005.GB2292@linux.vnet.ibm.com> <20110607125809.GA23214@somewhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110607125809.GA23214@somewhere> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1901 Lines: 40 On Tue, Jun 07, 2011 at 02:58:13PM +0200, Frederic Weisbecker wrote: > On Mon, Jun 06, 2011 at 09:40:05PM -0700, Paul E. McKenney wrote:> > > The bit I am missing is how to distinguish between spinlocks (where > > sleeping is illegal) and mutexes (where sleeping is perfectly fine). > > We could teach lockdep the difference, I suppose, but it is not clear > > to me that it is worth it. > > Ah, in fact it doesn't pass through any lockdep check. > > It's only a function called might_sleep() that is placed in functions > that can sleep. And inside might_sleep() it checks whether it is in a preemptible > area. So it's actually locking-agnostic, it only relies on the preempt_count > and some more for the preempt rcu cases. > > I think it is called CONFIG_DEBUG_SPINLOCK_SLEEP because it was first used > for spinlock debugging purposes. But then it has a broader use now: sleep > inside preemptible section, sleep inside interrupts, sleep inside rcu. But the __might_sleep() function can only differentiate between spinlocks and sleeplocks if CONFIG_PREEMPT=y. > It certainly deserves a rename, like CONFIG_DEBUG_ILLEGAL_SLEEP. Hmmm... It already checks for sleeping in the middle of a preempt_disable() as well as in a spinlock critical section. So the need for a rename is independent of any RCU checking. > > In contrast, with RCU, this is straightforward -- check for rcu_sched > > and rcu_bh, but not SRCU. Actually it makes sense to keep the checks in rcu_note_context_switch(), as there are places that call schedule() directly without a might_sleep(). Perhaps having checks in both places is the correct approach? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/