From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758790AbeD0QnJ (ORCPT ); Fri, 27 Apr 2018 12:43:09 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45654 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758562AbeD0QnG (ORCPT ); Fri, 27 Apr 2018 12:43:06 -0400 Date: Fri, 27 Apr 2018 09:44:16 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Joel Fernandes , linux-kernel@vger.kernel.org, Peter Zilstra , Ingo Molnar , Mathieu Desnoyers , Tom Zanussi , Namhyung Kim , Thomas Glexiner , Boqun Feng , Frederic Weisbecker , Randy Dunlap , Masami Hiramatsu , Fenguang Wu , Baohong Liu , Vedang Patel , kernel-team@android.com Subject: Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on Reply-To: paulmck@linux.vnet.ibm.com References: <20180427042656.190746-1-joelaf@google.com> <20180427155701.GL26088@linux.vnet.ibm.com> <20180427121330.40b7ef15@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180427121330.40b7ef15@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18042716-0040-0000-0000-000004233FF9 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008932; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000257; SDB=6.01024091; UDB=6.00522853; IPR=6.00803321; MB=3.00020809; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-27 16:43:04 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042716-0041-0000-0000-000008294210 Message-Id: <20180427164416.GN26088@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-27_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804270160 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 27, 2018 at 12:13:30PM -0400, Steven Rostedt wrote: > On Fri, 27 Apr 2018 08:57:01 -0700 > "Paul E. McKenney" wrote: > > > > + if (preempt_on) { \ > > > + WARN_ON_ONCE(in_nmi()); /* no srcu from nmi */ \ > > > > Very good on this check, thank you! > > I think you need to return and not call the read lock. Works for me either way, at least assuming that the splat actually gets printed. ;-) > if (WARN_ON_ONCE(in_nmi())) > return; > > > > > > + idx = srcu_read_lock(&tracepoint_srcu); \ > > > > Hmmm... Do I need to create a _notrace variant of srcu_read_lock() > > and srcu_read_unlock()? > > I think so. OK, please see the (untested) patch below. Of course, srcu_read_lock_notrace() invokes __srcu_read_lock(), which looks as follows: int __srcu_read_lock(struct srcu_struct *sp) { int idx; idx = READ_ONCE(sp->srcu_idx) & 0x1; this_cpu_inc(sp->sda->srcu_lock_count[idx]); smp_mb(); /* B */ /* Avoid leaking the critical section. */ return idx; } Do I also need to make a notrace version of __srcu_read_lock()? Same question for __srcu_read_unlock(), which is similar. If so, assuming that there is no need for a notrace variant of this_cpu_inc() and smp_mb(), I suppose I could simply macro-ize the internals in both cases, but perhaps you have a better approach. Thanx, Paul ------------------------------------------------------------------------ diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 91494d7e8e41..e2e2cf05a6eb 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -195,6 +195,16 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) return retval; } +/* Used by tracing, cannot be traced and cannot invoke lockdep. */ +static inline notrace int +srcu_read_lock_notrace(struct srcu_struct *sp) __acquires(sp) +{ + int retval; + + retval = __srcu_read_lock(sp); + return retval; +} + /** * srcu_read_unlock - unregister a old reader from an SRCU-protected structure. * @sp: srcu_struct in which to unregister the old reader. @@ -205,6 +215,13 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp) { + __srcu_read_unlock(sp, idx); +} + +/* Used by tracing, cannot be traced and cannot call lockdep. */ +static inline notrace void +srcu_read_unlock_notrace(struct srcu_struct *sp, int idx) __releases(sp) +{ rcu_lock_release(&(sp)->dep_map); __srcu_read_unlock(sp, idx); }