Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933860AbbGHQIH (ORCPT ); Wed, 8 Jul 2015 12:08:07 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:41129 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759315AbbGHQIE (ORCPT ); Wed, 8 Jul 2015 12:08:04 -0400 Date: Wed, 8 Jul 2015 18:07:50 +0200 From: Peter Zijlstra To: Mikulas Patocka Cc: Andy Lutomirski , Paul Mackerras , Arnaldo Carvalho de Melo , Kees Cook , Andrea Arcangeli , Vince Weaver , "hillf.zj" , Valdis Kletnieks , linux-kernel@vger.kernel.org Subject: Re: Kernel broken on processors without performance counters Message-ID: <20150708160750.GQ19282@twins.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1608 Lines: 41 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) || atomic_read(&mm->context.perf_rdpmc_allowed)) cr4_set_bits(X86_CR4_PCE); else -- 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/