From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754261AbbAaQS5 (ORCPT ); Sat, 31 Jan 2015 11:18:57 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:57499 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754027AbbAaQS4 (ORCPT ); Sat, 31 Jan 2015 11:18:56 -0500 Date: Sat, 31 Jan 2015 08:18:50 -0800 From: "Paul E. McKenney" To: Andy Lutomirski Cc: Sasha Levin , Borislav Petkov , X86 ML , Linus Torvalds , "linux-kernel@vger.kernel.org" , Peter Zijlstra , Tony Luck , Andi Kleen , Josh Triplett , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker Subject: Re: [PATCH] x86, traps: Fix ist_enter from userspace Message-ID: <20150131161850.GX19109@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <54CC2FA8.7070006@oracle.com> <261ebee6aee55a4724746d0d7024697013c40a08.1422709102.git.luto@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <261ebee6aee55a4724746d0d7024697013c40a08.1422709102.git.luto@amacapital.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15013116-0013-0000-0000-0000086291A6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 31, 2015 at 05:01:34AM -0800, Andy Lutomirski wrote: > context_tracking_user_exit() has no effect if in_interrupt() returns true, > so ist_enter() didn't work. Fix it by calling exception_enter(), and thus > context_tracking_user_exit(), before incrementing the preempt count. > > This also adds an assertion that will catch the problem reliably if > CONFIG_PROVE_RCU=y to help prevent the bug from being reintroduced. > > Fixes: 959274753857 x86, traps: Track entry into and exit from IST context > Reported-by: Sasha Levin > Signed-off-by: Andy Lutomirski > --- > arch/x86/kernel/traps.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index 7176f84f95a4..c74f2f5652da 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -110,15 +110,11 @@ static inline void preempt_conditional_cli(struct pt_regs *regs) > > enum ctx_state ist_enter(struct pt_regs *regs) > { > - /* > - * We are atomic because we're on the IST stack (or we're on x86_32, > - * in which case we still shouldn't schedule. > - */ > - preempt_count_add(HARDIRQ_OFFSET); > + enum ctx_state prev_state; > > if (user_mode_vm(regs)) { > /* Other than that, we're just an exception. */ > - return exception_enter(); > + prev_state = exception_enter(); > } else { > /* > * We might have interrupted pretty much anything. In > @@ -127,12 +123,27 @@ enum ctx_state ist_enter(struct pt_regs *regs) > * but we need to notify RCU. > */ > rcu_nmi_enter(); > - return IN_KERNEL; /* the value is irrelevant. */ > + prev_state = IN_KERNEL; /* the value is irrelevant. */ > } > + > + /* > + * We are atomic because we're on the IST stack (or we're on x86_32, > + * in which case we still shouldn't schedule). > + * > + * This must be after exception_enter(), because exception_enter() > + * won't do anything if in_interrupt() returns true. > + */ > + preempt_count_add(HARDIRQ_OFFSET); So the reason we need this here is that ist_exit() does not have access to the bits tested by user_mode_vm()? Or is the idea to avoid an additional test in ist_exit()? (Wondering why this isn't in the above "else" clause.) Thanx, Paul > + > + /* This code is a bit fragile. Test it. */ > + rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work"); > + > + return prev_state; > } > > void ist_exit(struct pt_regs *regs, enum ctx_state prev_state) > { > + /* Must be before exception_exit. */ > preempt_count_sub(HARDIRQ_OFFSET); > > if (user_mode_vm(regs)) > -- > 2.1.0 >