Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755081AbbLDXu2 (ORCPT ); Fri, 4 Dec 2015 18:50:28 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:38913 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753567AbbLDXtt (ORCPT ); Fri, 4 Dec 2015 18:49:49 -0500 X-IBM-Helo: d03dlp02.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org 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" Subject: [PATCH tip/core/rcu 3/8] documentation: Cover requirements controlling stall warnings Date: Fri, 4 Dec 2015 15:50:21 -0800 Message-Id: <1449273026-23633-3-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 2.5.2 In-Reply-To: <20151204234952.GA22805@linux.vnet.ibm.com> References: <20151204234952.GA22805@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15120423-0005-0000-0000-00001A5B5EC7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4801 Lines: 100 This commit adds verbiage on boot and sysfs parameters that can be used to control RCU CPU stall warnings, both to change the timeout and to suppress these warnings entirely. Signed-off-by: Paul E. McKenney --- .../RCU/Design/Requirements/Requirements.html | 25 +++++++++++++++++++++- .../RCU/Design/Requirements/Requirements.htmlx | 25 +++++++++++++++++++++- 2 files changed, 48 insertions(+), 2 deletions(-) diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index cda58d46f751..12f9d1555db3 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -1618,12 +1618,35 @@ guard against mishaps and misuse: supplied the needed patch.
  • An infinite loop in an RCU read-side critical section will - eventually trigger an RCU CPU stall warning splat. + eventually trigger an RCU CPU stall warning splat, with + the duration of “eventually” being controlled by the + RCU_CPU_STALL_TIMEOUT Kconfig option, or, + alternatively, by the + rcupdate.rcu_cpu_stall_timeout boot/sysfs + parameter. However, RCU is not obligated to produce this splat unless there is a grace period waiting on that particular RCU read-side critical section. +

    + Some extreme workloads might intentionally delay + RCU grace periods, and systems running those workloads can + be booted with rcupdate.rcu_cpu_stall_suppress + to suppress the splats. + This kernel parameter may also be set via sysfs. + Furthermore, RCU CPU stall warnings are counter-productive + during sysrq dumps and during panics. + RCU therefore supplies the rcu_sysrq_start() and + rcu_sysrq_end() API members to be called before + and after long sysrq dumps. + RCU also supplies the rcu_panic() notifier that is + automatically invoked at the beginning of a panic to suppress + further RCU CPU stall warnings. + +

    This requirement made itself known in the early 1990s, pretty much the first time that it was necessary to debug a CPU stall. + That said, the initial implementation in DYNIX/ptx was quite + generic in comparison with that of Linux.

  • Although it would be very good to detect pointers leaking out of RCU read-side critical sections, there is currently no good way of doing this. diff --git a/Documentation/RCU/Design/Requirements/Requirements.htmlx b/Documentation/RCU/Design/Requirements/Requirements.htmlx index 859a39534286..20bc84557f05 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.htmlx +++ b/Documentation/RCU/Design/Requirements/Requirements.htmlx @@ -1777,12 +1777,35 @@ guard against mishaps and misuse: supplied the needed patch.
  • An infinite loop in an RCU read-side critical section will - eventually trigger an RCU CPU stall warning splat. + eventually trigger an RCU CPU stall warning splat, with + the duration of “eventually” being controlled by the + RCU_CPU_STALL_TIMEOUT Kconfig option, or, + alternatively, by the + rcupdate.rcu_cpu_stall_timeout boot/sysfs + parameter. However, RCU is not obligated to produce this splat unless there is a grace period waiting on that particular RCU read-side critical section. +

    + Some extreme workloads might intentionally delay + RCU grace periods, and systems running those workloads can + be booted with rcupdate.rcu_cpu_stall_suppress + to suppress the splats. + This kernel parameter may also be set via sysfs. + Furthermore, RCU CPU stall warnings are counter-productive + during sysrq dumps and during panics. + RCU therefore supplies the rcu_sysrq_start() and + rcu_sysrq_end() API members to be called before + and after long sysrq dumps. + RCU also supplies the rcu_panic() notifier that is + automatically invoked at the beginning of a panic to suppress + further RCU CPU stall warnings. + +

    This requirement made itself known in the early 1990s, pretty much the first time that it was necessary to debug a CPU stall. + That said, the initial implementation in DYNIX/ptx was quite + generic in comparison with that of Linux.

  • Although it would be very good to detect pointers leaking out of RCU read-side critical sections, there is currently no good way of doing this. -- 2.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/