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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Fri, 28 Jun 2019 18:20:57 +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 x5SHKuk048431520 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 28 Jun 2019 17:20:56 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 25145B2064; Fri, 28 Jun 2019 17:20:56 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 075A1B205F; Fri, 28 Jun 2019 17:20:56 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Fri, 28 Jun 2019 17:20:55 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 9E5DB16C5DE8; Fri, 28 Jun 2019 10:20:56 -0700 (PDT) Date: Fri, 28 Jun 2019 10:20:56 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Scott Wood , Joel Fernandes , Steven Rostedt , Sebastian Andrzej Siewior , 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: <20190627155506.GU26519@linux.ibm.com> <20190627173831.GW26519@linux.ibm.com> <20190627181638.GA209455@google.com> <20190627184107.GA26519@linux.ibm.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190628160408.GH32547@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19062817-0060-0000-0000-00000356C2C4 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011347; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01224567; UDB=6.00644528; IPR=6.01005760; MB=3.00027510; MTD=3.00000008; XFM=3.00000015; UTC=2019-06-28 17:21:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19062817-0061-0000-0000-000049F1045C Message-Id: <20190628172056.GW26519@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-28_08:,, 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=520 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906280198 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 28, 2019 at 06:04:08PM +0200, Peter Zijlstra wrote: > On Fri, Jun 28, 2019 at 08:54:04AM -0700, Paul E. McKenney wrote: > > Thank you! Plus it looks like scheduler_ipi() takes an early exit if > > ->wake_list is empty, regardless of TIF_NEED_RESCHED, right? > > Yes, TIF_NEED_RESCHED is checked in the interrupt return path. OK, got it. So the following sequence would be a valid way to get the scheduler's attention on the current CPU shortly after interrupts are re-enabled, even if the current CPU is already holding some rq or pi locks, correct? set_tsk_need_resched(current); set_preempt_need_resched(); smp_send_reschedule(smp_processor_id()); Thanx, Paul