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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 20 Jun 2019 23:25:04 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5KMP3O044761490 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 20 Jun 2019 22:25:03 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BD847B205F; Thu, 20 Jun 2019 22:25:03 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AA9BDB2067; Thu, 20 Jun 2019 22:25:03 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 20 Jun 2019 22:25:03 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id B7EF816C2FA6; Thu, 20 Jun 2019 15:25:05 -0700 (PDT) Date: Thu, 20 Jun 2019 15:25:05 -0700 From: "Paul E. McKenney" To: Scott Wood Cc: Sebastian Andrzej Siewior , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Juri Lelli , Clark Williams , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH RT 3/4] rcu: unlock special: Treat irq and preempt disabled the same Reply-To: paulmck@linux.ibm.com References: <20190619011908.25026-1-swood@redhat.com> <20190619011908.25026-4-swood@redhat.com> <20190620211005.GW26519@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19062022-0064-0000-0000-000003F08FA7 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011299; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01220891; UDB=6.00642289; IPR=6.01002030; MB=3.00027398; MTD=3.00000008; XFM=3.00000015; UTC=2019-06-20 22:25:07 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19062022-0065-0000-0000-00003DF6536E Message-Id: <20190620222505.GB26519@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-20_15:,, 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-1906200159 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 20, 2019 at 04:59:30PM -0500, Scott Wood wrote: > On Thu, 2019-06-20 at 14:10 -0700, Paul E. McKenney wrote: > > On Tue, Jun 18, 2019 at 08:19:07PM -0500, Scott Wood wrote: > > > [Note: Just before posting this I noticed that the invoke_rcu_core stuff > > > is part of the latest RCU pull request, and it has a patch that > > > addresses this in a more complicated way that appears to deal with the > > > bare irq-disabled sequence as well. > > > > Far easier to deal with it than to debug the lack of it. ;-) > > > > > Assuming we need/want to support such sequences, is the > > > invoke_rcu_core() call actually going to result in scheduling any > > > sooner? resched_curr() just does the same setting of need_resched > > > when it's the same cpu. > > > ] > > > > Yes, invoke_rcu_core() can in some cases invoke the scheduler sooner. > > Setting the CPU-local bits might not have effect until the next interrupt. > > Maybe I'm missing something, but I don't see how (in the non-use_softirq > case). It just calls wake_up_process(), which in resched_curr() will set > need_resched but not do an IPI-to-self. The common non-rt case will be use_softirq. Or are you referring specifically to this block of code in current -rcu? } else if (exp && irqs_were_disabled && !use_softirq && !t->rcu_read_unlock_special.b.deferred_qs) { // Safe to awaken and we get no help from enabling // irqs, unlike bh/preempt. invoke_rcu_core(); Thanx, Paul