From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751379AbdAXVzJ (ORCPT ); Tue, 24 Jan 2017 16:55:09 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50744 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751001AbdAXVvh (ORCPT ); Tue, 24 Jan 2017 16:51:37 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" , Petr Mladek Subject: [PATCH v3 tip/core/rcu 09/18] rcu: Once again use NMI-based stack traces in stall warnings Date: Tue, 24 Jan 2017 13:51:20 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170124215111.GB2269@linux.vnet.ibm.com> References: <20170124215111.GB2269@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17012421-0008-0000-0000-000007032D80 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006492; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000200; SDB=6.00812181; UDB=6.00396064; IPR=6.00589599; BA=6.00005085; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014031; XFM=3.00000011; UTC=2017-01-24 21:51:34 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17012421-0009-0000-0000-00003F48929A Message-Id: <1485294689-11485-9-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-01-24_17:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1701240129 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit is for all intents and purposes a revert of bc1dce514e9b ("rcu: Don't use NMIs to dump other CPUs' stacks"). The reason to suppose that this can now safely be reverted is the presence of 42a0bb3f7138 ("printk/nmi: generic solution for safe printk in NMI"), which is said to have made NMI-based stack dumps safe. However, this reversion keeps one nice property of bc1dce514e9b ("rcu: Don't use NMIs to dump other CPUs' stacks"), namely that only those CPUs blocking the grace period are dumped. The new trigger_single_cpu_backtrace() is used to make this happen, as suggested by Josh Poimboeuf. Reported-by: Vince Weaver Signed-off-by: Paul E. McKenney Cc: Petr Mladek Cc: Peter Zijlstra Reviewed-by: Josh Poimboeuf Reviewed-by: Petr Mladek Reviewed-by: Josh Triplett --- kernel/rcu/tree.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5a4aaad75e76..d7b63b88434b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1278,7 +1278,10 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp) } /* - * Dump stacks of all tasks running on stalled CPUs. + * Dump stacks of all tasks running on stalled CPUs. First try using + * NMIs, but fall back to manual remote stack tracing on architectures + * that don't support NMI-based stack dumps. The NMI-triggered stack + * traces are more accurate because they are printed by the target CPU. */ static void rcu_dump_cpu_stacks(struct rcu_state *rsp) { @@ -1288,11 +1291,10 @@ static void rcu_dump_cpu_stacks(struct rcu_state *rsp) rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); - if (rnp->qsmask != 0) { - for_each_leaf_node_possible_cpu(rnp, cpu) - if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) + for_each_leaf_node_possible_cpu(rnp, cpu) + if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) + if (!trigger_single_cpu_backtrace(cpu)) dump_cpu_task(cpu); - } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } } -- 2.5.2