From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: linux-next: PowerPC WARN_ON_ONCE() after merge of the final tree (tip related) Date: Fri, 16 Apr 2010 11:51:30 +1000 Message-ID: <1271382690.13059.169.camel@pasglop> References: <20100415161214.04637496.sfr@canb.auug.org.au> <20100415064940.GA9240@elte.hu> <20100414.235557.123118153.davem@davemloft.net> <20100415073256.GG9240@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from gate.crashing.org ([63.228.1.57]:46673 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758207Ab0DPBxV (ORCPT ); Thu, 15 Apr 2010 21:53:21 -0400 In-Reply-To: <20100415073256.GG9240@elte.hu> Sender: linux-next-owner@vger.kernel.org List-ID: To: Ingo Molnar Cc: David Miller , sfr@canb.auug.org.au, peterz@infradead.org, fweisbec@gmail.com, linux-kernel@vger.kernel.org, linux-next@vger.kernel.org, hpa@zytor.com, tglx@linutronix.de, linuxppc-dev@lists.ozlabs.org On Thu, 2010-04-15 at 09:32 +0200, Ingo Molnar wrote: > It trades robustness for slightly better space/code efficiency. > > Such a trap based mechanism exists on x86 as well and we use it for BUG_ON(). > We intentionally dont use it to generate warnings and dont override __WARN(), > because it would blow up way too often when a warning triggers in some > sensitive codepath that cannot take a trap. > > Anyway, the warning obviously has to be fixed - but the boot crash itself is > PowerPC's own doing. Well, yes and no, as I explained in a separate branch of that thread. We indeed can't cope with a WARN in that spot because it goes recursive. Now the reason we have this double-enable is due afaik to the way I implemented IRQ trace, because things like syscalls basically force-enable IRQs on powerpc and I don't necessarily have tracking informations in the exception return path of what the "old" value was. I need to double check what the exact scenario here is and whether I can fix it but it's one of those cases where what lockdep is warning about isn't actually an error I believe. Cheers, Ben.