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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 6 Jun 2019 07:05:12 +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 x5665BTq20513192 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 6 Jun 2019 06:05:11 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id ECEC0B2068; Thu, 6 Jun 2019 06:05:10 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C47B4B206A; Thu, 6 Jun 2019 06:05:10 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.226.118]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 6 Jun 2019 06:05:10 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 1841416C15CF; Wed, 5 Jun 2019 23:05:11 -0700 (PDT) Date: Wed, 5 Jun 2019 23:05:11 -0700 From: "Paul E. McKenney" To: Herbert Xu Cc: Alan Stern , Boqun Feng , Linus Torvalds , Frederic Weisbecker , Fengguang Wu , LKP , LKML , Netdev , "David S. Miller" , Andrea Parri , Luc Maranget , Jade Alglave Subject: Re: rcu_read_lock lost its compiler barrier Reply-To: paulmck@linux.ibm.com References: <20190603200301.GM28207@linux.ibm.com> <20190606045109.zjfxxbkzq4wb64bj@gondor.apana.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190606045109.zjfxxbkzq4wb64bj@gondor.apana.org.au> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19060606-0060-0000-0000-0000034CD5B4 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011222; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01213919; UDB=6.00638066; IPR=6.00994998; MB=3.00027202; MTD=3.00000008; XFM=3.00000015; UTC=2019-06-06 06:05:15 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19060606-0061-0000-0000-000049A75F2D Message-Id: <20190606060511.GA28207@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-06_05:,, 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-1906060045 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 06, 2019 at 12:51:09PM +0800, Herbert Xu wrote: > On Tue, Jun 04, 2019 at 10:44:18AM -0400, Alan Stern wrote: > > > > Currently the LKMM says the test is allowed and there is a data race, > > but this answer clearly is wrong since it would violate the RCU > > guarantee. > > Thank you! This is what I tried to say all along in this thread > but you expressed it in a much better way :) In case you were wondering, the reason that I was giving you such a hard time was that from what I could see, you were pushing for no {READ,WRITE}_ONCE() at all. ;-) Thanx, Paul