From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0288C28CC3 for ; Thu, 30 May 2019 14:52:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3A2425BB1 for ; Thu, 30 May 2019 14:52:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727216AbfE3Owj (ORCPT ); Thu, 30 May 2019 10:52:39 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:43988 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725961AbfE3Owi (ORCPT ); Thu, 30 May 2019 10:52:38 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x4UEppeh105228 for ; Thu, 30 May 2019 10:52:37 -0400 Received: from e14.ny.us.ibm.com (e14.ny.us.ibm.com [129.33.205.204]) by mx0a-001b2d01.pphosted.com with ESMTP id 2stgu3sjj9-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 30 May 2019 10:52:37 -0400 Received: from localhost by e14.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 30 May 2019 15:52:36 +0100 Received: from b01cxnp23034.gho.pok.ibm.com (9.57.198.29) by e14.ny.us.ibm.com (146.89.104.201) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 30 May 2019 15:52:31 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x4UEqUFK25755956 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 May 2019 14:52:30 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 04FA0B2064; Thu, 30 May 2019 14:52:30 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D63EDB206C; Thu, 30 May 2019 14:52:29 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.216]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 30 May 2019 14:52:29 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 5E4BC16C5DA0; Thu, 30 May 2019 07:52:31 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, 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, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, byungchul.park@lge.com, kernel-team@android.com, "Paul E . McKenney" Subject: [PATCH tip/core/rcu 10/12] rcu: Add checks for dynticks counters in rcu_is_cpu_rrupt_from_idle() Date: Thu, 30 May 2019 07:52:27 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190530145204.GA28526@linux.ibm.com> References: <20190530145204.GA28526@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19053014-0052-0000-0000-000003C912BD X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011185; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01210783; UDB=6.00636156; IPR=6.00991817; MB=3.00027120; MTD=3.00000008; XFM=3.00000015; UTC=2019-05-30 14:52:35 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19053014-0053-0000-0000-0000611A106C Message-Id: <20190530145229.29565-10-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-30_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905300106 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Joel Fernandes (Google)" It would be good to combine the dynticks and dynticks_nesting counters in order to simplify the code. Unfortunately, there are concerns about usermode upcalls appearing to RCU as half of an interrupt, as Byungchul learned [1]. The "half" in "half interrupt" is due to an unpaired rcu_irq_enter(): Normally, each rcu_irq_enter() has a later call to rcu_irq_exit(). Out of an abundance of caution, Paul added warnings [2] in the RCU code which if not fired by 2021 will be interpreted as meaning that this half-interrupt scenario cannot happen any more, thus permitting simplification of this code. In the meantime, this commit makes the following changes: (1) Combining these two counters requires that rcu_rrupt_from_idle() is invoked only from hard-interrupt contexts as discussed here [3]. This commit therefore adds the required lockdep_assert_in_irq() to check this constraint. (2) Furthermore, rcu_rrupt_from_idle() is not explicit about how it is using the counters which can lead to weird future bugs. This commit therefore adds comments indicating the meaning and use of each counter. (3) Lastly, this commit checks for counter underflows as another check that half interrupts don't occur. (Previously, the function would simply return true upon underflow.) All these checks checks are NOOPs if PROVE_LOCKING (and thus PROVE_RCU) are disabled. [1] https://lore.kernel.org/patchwork/patch/952349/ [2] Commit e11ec65cc8d6 ("rcu: Add warning to detect half-interrupts") [3] https://lore.kernel.org/lkml/20190312150514.GB249405@google.com/ Cc: byungchul.park@lge.com Cc: kernel-team@android.com Cc: rcu@vger.kernel.org Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 7822a2e1370d..b9629cf08f94 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -376,16 +376,29 @@ static void __maybe_unused rcu_momentary_dyntick_idle(void) } /** - * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle + * rcu_is_cpu_rrupt_from_idle - see if interrupted from idle * - * If the current CPU is idle or running at a first-level (not nested) + * If the current CPU is idle and running at a first-level (not nested) * interrupt from idle, return true. The caller must have at least * disabled preemption. */ static int rcu_is_cpu_rrupt_from_idle(void) { - return __this_cpu_read(rcu_data.dynticks_nesting) <= 0 && - __this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 1; + /* Called only from within the scheduling-clock interrupt */ + lockdep_assert_in_irq(); + + /* Check for counter underflows */ + RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0, + "RCU dynticks_nesting counter underflow!"); + RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0, + "RCU dynticks_nmi_nesting counter underflow/zero!"); + + /* Are we at first interrupt nesting level? */ + if (__this_cpu_read(rcu_data.dynticks_nmi_nesting) != 1) + return false; + + /* Does CPU appear to be idle from an RCU standpoint? */ + return __this_cpu_read(rcu_data.dynticks_nesting) == 0; } #define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch. */ -- 2.17.1