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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 25 Jun 2018 16:45:04 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w5PKj3VA59900068 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 25 Jun 2018 20:45:03 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 12A22B206B; Mon, 25 Jun 2018 16:44:58 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id F2086B205F; Mon, 25 Jun 2018 16:44:57 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.159]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 25 Jun 2018 16:44:57 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 10F2316CA093; Mon, 25 Jun 2018 13:47:08 -0700 (PDT) Date: Mon, 25 Jun 2018 13:47:08 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Joel Fernandes , Byungchul Park , Byungchul Park , jiangshanlai@gmail.com, josh@joshtriplett.org, Mathieu Desnoyers , linux-kernel@vger.kernel.org, kernel-team@lge.com, luto@kernel.org Subject: Re: [RFC 2/2] rcu: Remove ->dynticks_nmi_nesting from struct rcu_dynticks Reply-To: paulmck@linux.vnet.ibm.com References: <20180620164902.GW3593@linux.vnet.ibm.com> <20180622055659.GA255098@joelaf.mtv.corp.google.com> <20180622132843.GN3593@linux.vnet.ibm.com> <20180622181916.GA13628@joelaf.mtv.corp.google.com> <20180622143247.781028b1@gandalf.local.home> <20180622200548.GA114655@joelaf.mtv.corp.google.com> <20180625082824.GB21377@X58A-UD3R> <20180625163951.GA52646@joelaf.mtv.corp.google.com> <20180625162557.7140664c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180625162557.7140664c@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18062520-0040-0000-0000-000004450465 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009254; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01052261; UDB=6.00539424; IPR=6.00830186; MB=3.00021853; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-25 20:45:06 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062520-0041-0000-0000-0000084B19FA Message-Id: <20180625204708.GS3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-25_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=749 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1806250227 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 25, 2018 at 04:25:57PM -0400, Steven Rostedt wrote: > On Mon, 25 Jun 2018 09:39:51 -0700 > Joel Fernandes wrote: > > > For whatever its worth, I made some notes of what I understood from reading > > the code and old posts because I was sure I would otherwise forget > > everything: > > http://www.joelfernandes.org/linuxinternals/2018/06/15/rcu-dynticks.html > > Nice write up. I may point some people to this ;-) > > Anyway "complications due to nested NMIs (yes NMIs can nest!)" > > What arch allows for NMIs to nest. Because we don't let that happen on > x86, and there's code that I know of that is called by NMIs that is not > re-entrant, and can crash if we allow for NMIs to nest. For example > "in_nmi()" will not show that we are in_nmi() if we allow for nesting > of NMIs. It has a single bit that gets incremented when we enter NMI > code, and cleared when we leave it. Last I checked with Andy Lutomirski, there are a number of things that, though not NMIs, act like NMIs and that can interrupt each others' handlers. This is on x86. Thanx, Paul