Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759287AbbGHRiT (ORCPT ); Wed, 8 Jul 2015 13:38:19 -0400 Received: from mail-la0-f51.google.com ([209.85.215.51]:36520 "EHLO mail-la0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758344AbbGHRiR (ORCPT ); Wed, 8 Jul 2015 13:38:17 -0400 MIME-Version: 1.0 In-Reply-To: <20150708160750.GQ19282@twins.programming.kicks-ass.net> References: <20150708160750.GQ19282@twins.programming.kicks-ass.net> From: Andy Lutomirski Date: Wed, 8 Jul 2015 10:37:55 -0700 Message-ID: Subject: Re: Kernel broken on processors without performance counters To: Peter Zijlstra Cc: Mikulas Patocka , Paul Mackerras , Arnaldo Carvalho de Melo , Kees Cook , Andrea Arcangeli , Vince Weaver , "hillf.zj" , Valdis Kletnieks , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1933 Lines: 48 On Wed, Jul 8, 2015 at 9:07 AM, Peter Zijlstra wrote: > On Wed, Jul 08, 2015 at 11:17:38AM -0400, Mikulas Patocka wrote: >> Hi >> >> I found out that the patch a66734297f78707ce39d756b656bfae861d53f62 breaks >> the kernel on processors without performance counters, such as AMD K6-3. >> Reverting the patch fixes the problem. >> >> The static key rdpmc_always_available somehow gets set (I couldn't really >> find out what is setting it, the function set_attr_rdpmc is not executed), >> cr4_set_bits(X86_CR4_PCE) is executed and that results in a crash on boot >> when attempting to execute init, because the proecssor doesn't support >> that bit in CR4. > > Urgh, the static key trainwreck bites again. > > One is not supposed to mix static_key_true() and STATIC_KEY_INIT_FALSE. > > Does this make it go again? > > --- > arch/x86/include/asm/mmu_context.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h > index 5e8daee7c5c9..804a3a6030ca 100644 > --- a/arch/x86/include/asm/mmu_context.h > +++ b/arch/x86/include/asm/mmu_context.h > @@ -23,7 +23,7 @@ extern struct static_key rdpmc_always_available; > > static inline void load_mm_cr4(struct mm_struct *mm) > { > - if (static_key_true(&rdpmc_always_available) || > + if (static_key_false(&rdpmc_always_available) || In what universe is "static_key_false" a reasonable name for a function that returns true if a static key is true? Can we rename that function? And could we maybe make static keys type safe? I.e. there would be a type that starts out true and a type that starts out false. --Andy -- 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/