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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 1 Jul 2019 17:01:05 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x61G14Yh10289498 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 1 Jul 2019 16:01:04 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B4085B2067; Mon, 1 Jul 2019 16:01:04 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 956AFB2066; Mon, 1 Jul 2019 16:01:04 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 1 Jul 2019 16:01:04 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 7054916C0B88; Mon, 1 Jul 2019 09:01:07 -0700 (PDT) Date: Mon, 1 Jul 2019 09:01:07 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Sebastian Andrzej Siewior , Scott Wood , Joel Fernandes , Steven Rostedt , rcu , LKML , Thomas Gleixner , Ingo Molnar , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs Reply-To: paulmck@linux.ibm.com References: <13761fee4b71cc004ad0d6709875ce917ff28fce.camel@redhat.com> <20190627203612.GD26519@linux.ibm.com> <20190628141522.GF3402@hirez.programming.kicks-ass.net> <20190628155404.GV26519@linux.ibm.com> <20190628160408.GH32547@worktop.programming.kicks-ass.net> <20190628172056.GW26519@linux.ibm.com> <20190701094215.GR3402@hirez.programming.kicks-ass.net> <20190701102442.35grdpcsbrwyyaco@linutronix.de> <20190701122305.GB26519@linux.ibm.com> <20190701140053.GV3402@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190701140053.GV3402@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19070116-0060-0000-0000-000003579D17 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011360; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01225960; UDB=6.00645376; IPR=6.01007172; MB=3.00027538; MTD=3.00000008; XFM=3.00000015; UTC=2019-07-01 16:01:09 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19070116-0061-0000-0000-000049F9B055 Message-Id: <20190701160107.GG26519@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-01_10:,, 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=830 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907010192 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 01, 2019 at 04:00:53PM +0200, Peter Zijlstra wrote: > On Mon, Jul 01, 2019 at 05:23:05AM -0700, Paul E. McKenney wrote: > > On Mon, Jul 01, 2019 at 12:24:42PM +0200, Sebastian Andrzej Siewior wrote: > > > On 2019-07-01 11:42:15 [+0200], Peter Zijlstra wrote: > > > > I'm not sure if smp_send_reschedule() can be used as self-IPI, some > > > > hardware doesn't particularly like that IIRC. That is, hardware might > > > > only have interfaces to IPI _other_ CPUs, but not self. > > > > > > > > The normal scheduler code takes care to not call smp_send_reschedule() > > > > to self. > > > > > > and irq_work: > > > 471ba0e686cb1 ("irq_work: Do not raise an IPI when queueing work on the local CPU") > > > > OK, so it looks like I will need to use something else. But thank you > > for calling my attention to this commit. > > I think that commit is worded slight confusing -- sorry I should've paid > more attention. > > irq_work _does_ work locally, and arch_irq_work_raise() must self-IPI, > otherwise everything is horribly broken. > > But what happened, was that irq_work_queue() and irq_work_queue_on(.cpu > = smp_processor_id()) wasn't using the same code, and the latter would > try to self-IPI through arch_send_call_function_single_ipi(). > > Nick fixed that so that irq_work_queue() and irq_work_queue_on(.cpu = > smp_processor_id() now both use arch_raise_irq_work() and remote stuff > uses arch_send_call_function_single_ipi(). OK, thank you for looking into this! I therefore continue relying on IRQ work. Should there be problems with kernels not supporting IRQ work, and if there is a legitimate reason why they should not support IRQ work, I can look into things like timers for those kernels. Thanx, Paul