From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755463AbdDFSB7 (ORCPT ); Thu, 6 Apr 2017 14:01:59 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38803 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755366AbdDFSBt (ORCPT ); Thu, 6 Apr 2017 14:01:49 -0400 Date: Thu, 6 Apr 2017 11:01:39 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton Subject: Re: [PATCH 4/4] rcu: Fix dyntick-idle tracing Reply-To: paulmck@linux.vnet.ibm.com References: <20170406164237.874767449@goodmis.org> <20170406164432.500893989@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170406164432.500893989@goodmis.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17040618-0052-0000-0000-000001CB050D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006888; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00843989; UDB=6.00415921; IPR=6.00622190; BA=6.00005274; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014939; XFM=3.00000013; UTC=2017-04-06 18:01:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17040618-0053-0000-0000-00004FBDBBC3 Message-Id: <20170406180139.GF1600@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-06_14:,, 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=8.0.1-1702020001 definitions=main-1704060144 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 06, 2017 at 12:42:41PM -0400, Steven Rostedt wrote: > From: "Paul E. McKenney" > > The tracing subsystem started using rcu_irq_entry() and rcu_irq_exit() > (with my blessing) to allow the current _rcuidle alternative tracepoint > name to be dispensed with while still maintaining good performance. > Unfortunately, this causes RCU's dyntick-idle entry code's tracing to > appear to RCU like an interrupt that occurs where RCU is not designed > to handle interrupts. > > This commit fixes this problem by moving the zeroing of ->dynticks_nesting > after the offending trace_rcu_dyntick() statement, which narrows the > window of vulnerability to a pair of adjacent statements that are now > marked with comments to that effect. > > Link: http://lkml.kernel.org/r/20170405193928.GM1600@linux.vnet.ibm.com > > Reported-by: Steven Rostedt > Signed-off-by: Paul E. McKenney > Signed-off-by: Steven Rostedt (VMware) Acked-by: Paul E. McKenney Really confirming my Signed-off-by given Steven's changes, but whatever. ;-) Thanx, Paul > --- > kernel/rcu/tree.c | 48 +++++++++++++++++++++++------------------------- > 1 file changed, 23 insertions(+), 25 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 50fee7689e71..8b4d273331e4 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -57,6 +57,7 @@ > #include > #include > #include > +#include > > #include "tree.h" > #include "rcu.h" > @@ -771,25 +772,24 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) > } > > /* > - * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state > + * rcu_eqs_enter_common - current CPU is entering an extended quiescent state > * > - * If the new value of the ->dynticks_nesting counter now is zero, > - * we really have entered idle, and must do the appropriate accounting. > - * The caller must have disabled interrupts. > + * Enter idle, doing appropriate accounting. The caller must have > + * disabled interrupts. > */ > -static void rcu_eqs_enter_common(long long oldval, bool user) > +static void rcu_eqs_enter_common(bool user) > { > struct rcu_state *rsp; > struct rcu_data *rdp; > - RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);) > + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > > - trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting); > + trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0); > if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > !user && !is_idle_task(current)) { > struct task_struct *idle __maybe_unused = > idle_task(smp_processor_id()); > > - trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0); > + trace_rcu_dyntick(TPS("Error on entry: not idle task"), rdtp->dynticks_nesting, 0); > rcu_ftrace_dump(DUMP_ORIG); > WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", > current->pid, current->comm, > @@ -800,7 +800,10 @@ static void rcu_eqs_enter_common(long long oldval, bool user) > do_nocb_deferred_wakeup(rdp); > } > rcu_prepare_for_idle(); > - rcu_dynticks_eqs_enter(); > + stack_tracer_disable(); > + rdtp->dynticks_nesting = 0; /* Breaks tracing momentarily. */ > + rcu_dynticks_eqs_enter(); /* After this, tracing works again. */ > + stack_tracer_enable(); > rcu_dynticks_task_enter(); > > /* > @@ -821,19 +824,15 @@ static void rcu_eqs_enter_common(long long oldval, bool user) > */ > static void rcu_eqs_enter(bool user) > { > - long long oldval; > struct rcu_dynticks *rdtp; > > rdtp = this_cpu_ptr(&rcu_dynticks); > - oldval = rdtp->dynticks_nesting; > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > - (oldval & DYNTICK_TASK_NEST_MASK) == 0); > - if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) { > - rdtp->dynticks_nesting = 0; > - rcu_eqs_enter_common(oldval, user); > - } else { > + (rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); > + if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) > + rcu_eqs_enter_common(user); > + else > rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; > - } > } > > /** > @@ -892,19 +891,18 @@ void rcu_user_enter(void) > */ > void rcu_irq_exit(void) > { > - long long oldval; > struct rcu_dynticks *rdtp; > > RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!"); > rdtp = this_cpu_ptr(&rcu_dynticks); > - oldval = rdtp->dynticks_nesting; > - rdtp->dynticks_nesting--; > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > - rdtp->dynticks_nesting < 0); > - if (rdtp->dynticks_nesting) > - trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting); > - else > - rcu_eqs_enter_common(oldval, true); > + rdtp->dynticks_nesting < 1); > + if (rdtp->dynticks_nesting <= 1) { > + rcu_eqs_enter_common(true); > + } else { > + trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nesting, rdtp->dynticks_nesting - 1); > + rdtp->dynticks_nesting--; > + } > rcu_sysidle_enter(1); > } > > -- > 2.10.2 > >