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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 1 May 2019 20:12:14 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x41JCDbq29294592 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 1 May 2019 19:12:14 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C9711B205F; Wed, 1 May 2019 19:12:13 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9DD8AB2065; Wed, 1 May 2019 19:12:13 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.216]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 1 May 2019 19:12:13 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id A88BF16C1656; Wed, 1 May 2019 12:12:13 -0700 (PDT) Date: Wed, 1 May 2019 12:12:13 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, andrea.parri@amarulasolutions.com, rostedt@goodmis.org Subject: Re: Question about sched_setaffinity() Reply-To: paulmck@linux.ibm.com References: <20190427180246.GA15502@linux.ibm.com> <20190430100318.GP2623@hirez.programming.kicks-ass.net> <20190430105129.GA3923@linux.ibm.com> <20190430115551.GT2623@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190430115551.GT2623@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19050119-0040-0000-0000-000004E9B45D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011030; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000285; SDB=6.01197153; UDB=6.00627876; IPR=6.00978007; MB=3.00026686; MTD=3.00000008; XFM=3.00000015; UTC=2019-05-01 19:12:16 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19050119-0041-0000-0000-000008F5B899 Message-Id: <20190501191213.GX3923@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-01_09:,, 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=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-1905010119 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 30, 2019 at 01:55:51PM +0200, Peter Zijlstra wrote: > On Tue, Apr 30, 2019 at 03:51:30AM -0700, Paul E. McKenney wrote: > > > Then I'm not entirely sure how we can return 0 and not run on the > > > expected CPU. If we look at __set_cpus_allowed_ptr(), the only paths out > > > to 0 are: > > > > > > - if the mask didn't change > > > - if we already run inside the new mask > > > - if we migrated ourself with the stop-task > > > - if we're not in fact running > > > > > > That last case should never trigger in your circumstances, since @p == > > > current and current is obviously running. But for completeness, the > > > wakeup of @p would do the task placement in that case. > > > > Are there some diagnostics I could add that would help track this down, > > be it my bug or yours? > > Maybe limited function trace combined with the scheduling tracepoints > would give clue. > > Trouble is, I forever forget how to set that up properly :/ Maybe > something along these lines: > > $ trace-cmd record -p function_graph -g sched_setaffinity -g migration_cpu_stop -e > sched_migirate_task -e sched_switch -e sched_wakeup > > Also useful would be: > > echo 1 > /proc/sys/kernel/traceoff_on_warning > > which ensures the trace stops the moment we find fail. OK, what I did was to apply the patch at the end of this email to -rcu branch dev, then run rcutorture as follows: nohup tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 8 --duration 2 --configs "TRIVIAL" --bootargs "trace_event=sched:sched_switch,sched:sched_wakeup ftrace=function_graph ftrace_graph_filter=sched_setaffinity,migration_cpu_stop" This resulted in the console output that I placed here: http://www2.rdrop.com/~paulmck/submission/console.log.gz But I don't see calls to sched_setaffinity() or migration_cpu_stop(). Steve, is something else needed on the kernel command line in addition to the following? ftrace=function_graph ftrace_graph_filter=sched_setaffinity,migration_cpu_stop Thanx, Paul ------------------------------------------------------------------------ diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index da04b5073dc3..ceae80522d64 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -680,12 +680,18 @@ static struct rcu_torture_ops tasks_ops = { static void synchronize_rcu_trivial(void) { int cpu; + static int dont_trace; for_each_online_cpu(cpu) { - while (raw_smp_processor_id() != cpu) - rcutorture_sched_setaffinity(current->pid, - cpumask_of(cpu)); - WARN_ON_ONCE(raw_smp_processor_id() != cpu); + if (!READ_ONCE(dont_trace)) + tracing_on(); + rcutorture_sched_setaffinity(current->pid, cpumask_of(cpu)); + tracing_off(); + if (raw_smp_processor_id() != cpu) { + WRITE_ONCE(dont_trace, 1); + WARN_ON_ONCE(1); + ftrace_dump(DUMP_ALL); + } } } diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index caffee644932..edaf0ca22ff7 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3495,6 +3495,7 @@ void __init rcu_init(void) rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0); WARN_ON(!rcu_par_gp_wq); srcu_init(); + tracing_off(); } #include "tree_stall.h"