From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751313AbdILF1e (ORCPT ); Tue, 12 Sep 2017 01:27:34 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34178 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750751AbdILF1d (ORCPT ); Tue, 12 Sep 2017 01:27:33 -0400 Date: Mon, 11 Sep 2017 21:04:35 -0700 From: "Paul E. McKenney" To: Masami Hiramatsu Cc: Ingo Molnar , Steven Rostedt , linux-kernel@vger.kernel.org, Peter Zijlstra , Ananth N Mavinakayanahalli , Thomas Gleixner , "H . Peter Anvin" Subject: Re: [PATCH -tip v2] kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT Reply-To: paulmck@linux.vnet.ibm.com References: <150517861179.26279.7649250983151178165.stgit@devbox> <150517865165.26279.7811625865051741769.stgit@devbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <150517865165.26279.7811625865051741769.stgit@devbox> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17091205-0008-0000-0000-0000027E9A4A X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007711; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000227; SDB=6.00915792; UDB=6.00459813; IPR=6.00696024; BA=6.00005586; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017118; XFM=3.00000015; UTC=2017-09-12 05:27:31 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17091205-0009-0000-0000-000036ACA77E Message-Id: <20170912040435.GS3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-12_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1709120077 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 12, 2017 at 10:10:51AM +0900, Masami Hiramatsu wrote: > To enable jump optimized probe with CONFIG_PREEMPT, use > synchronize_rcu_tasks() to wait for all tasks preempted > on trampoline code back on track. > > Since the jump optimized kprobes can replace multiple > instructions, there can be tasks which are interrupted > on the 2nd (or 3rd) instructions. If the kprobe > replaces those instructions by a jump instruction, > when those tasks back to the interrupted place, it is > a middle of the jump instruction and causes a kernel > panic. > To avoid such tragedies in advance, kprobe optimizer > prepare a detour route using normal kprobe (e.g. > int3 breakpoint on x86), and wait for the tasks which > is interrrupted on such place by synchronize_sched() > when CONFIG_PREEMPT=n. > If CONFIG_PREEMPT=y, things be more complicated, because > such interrupted thread can be preempted (other thread > can be scheduled in interrupt handler.) So, kprobes > optimizer has to wait for those tasks scheduled normally. > In this case we can use synchronize_rcu_tasks() which > ensures that all preempted tasks back on track and > schedule it. > > Signed-off-by: Masami Hiramatsu Reviewed-by: Paul E. McKenney > --- > arch/Kconfig | 2 +- > kernel/kprobes.c | 18 +++++++++++++----- > 2 files changed, 14 insertions(+), 6 deletions(-) > > diff --git a/arch/Kconfig b/arch/Kconfig > index 2520ca5b42eb..d495c06ae961 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -90,7 +90,7 @@ config STATIC_KEYS_SELFTEST > config OPTPROBES > def_bool y > depends on KPROBES && HAVE_OPTPROBES > - depends on !PREEMPT > + select TASKS_RCU if PREEMPT > > config KPROBES_ON_FTRACE > def_bool y > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index a1606a4224e1..6243b8b02511 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -574,12 +574,20 @@ static void kprobe_optimizer(struct work_struct *work) > > /* > * Step 2: Wait for quiesence period to ensure all running interrupts > - * are done. Because optprobe may modify multiple instructions > - * there is a chance that Nth instruction is interrupted. In that > - * case, running interrupt can return to 2nd-Nth byte of jump > - * instruction. This wait is for avoiding it. > + * are done. Because optprobe may modify multiple instructions, > + * there is a chance that the Nth instruction is interrupted. In that > + * case, running interrupt can return to the Nth byte of jump > + * instruction. This can be avoided by waiting for returning of > + * such interrupts, since (until here) the first byte of the optimized > + * probe is already replaced with normal kprobe (sw breakpoint) and > + * all threads which reach to the probed address will hit it and > + * bypass the copied instructions instead of executing the original. > + * With CONFIG_PREEMPT, such interrupts can be preepmted. To wait > + * for such thread, we will use synchronize_rcu_tasks() which ensures > + * all preeempted tasks are scheduled normally (= not preempted.) > + * So we can ensure there is no threads preempted at probed address. > */ > - synchronize_sched(); > + synchronize_rcu_tasks(); > > /* Step 3: Optimize kprobes after quiesence period */ > do_optimize_kprobes(); >