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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 22 Jul 2019 17:15:54 +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 x6MGFrNI55312674 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 22 Jul 2019 16:15:54 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D2013B2067; Mon, 22 Jul 2019 16:15:53 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9308AB2064; Mon, 22 Jul 2019 16:15:53 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.189.166]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 22 Jul 2019 16:15:53 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 257E516C2E45; Mon, 22 Jul 2019 09:15:55 -0700 (PDT) Date: Mon, 22 Jul 2019 09:15:55 -0700 From: "Paul E. McKenney" To: Jason Gunthorpe Cc: "Michael S. Tsirkin" , Matthew Wilcox , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jasowang@redhat.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: RFC: call_rcu_outstanding (was Re: WARNING in __mmdrop) Reply-To: paulmck@linux.ibm.com References: <20190721044615-mutt-send-email-mst@kernel.org> <20190721081933-mutt-send-email-mst@kernel.org> <20190721131725.GR14271@linux.ibm.com> <20190721210837.GC363@bombadil.infradead.org> <20190721233113.GV14271@linux.ibm.com> <20190722035042-mutt-send-email-mst@kernel.org> <20190722115149.GY14271@linux.ibm.com> <20190722134152.GA13013@ziepe.ca> <20190722155235.GF14271@linux.ibm.com> <20190722160448.GH7607@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190722160448.GH7607@ziepe.ca> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19072216-2213-0000-0000-000003B44BB4 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011475; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01235885; UDB=6.00651341; IPR=6.01017236; MB=3.00027839; MTD=3.00000008; XFM=3.00000015; UTC=2019-07-22 16:16:01 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19072216-2214-0000-0000-00005F587017 Message-Id: <20190722161555.GJ14271@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-22_12:,, 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=846 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907220180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 22, 2019 at 01:04:48PM -0300, Jason Gunthorpe wrote: > On Mon, Jul 22, 2019 at 08:52:35AM -0700, Paul E. McKenney wrote: > > So why then is there a problem? > > I'm not sure there is a real problem, I thought Michael was just > asking how to design with RCU in the case where the user controls the > kfree_rcu?? > > Sounds like the answer is "don't worry about it" ? Unless you can force failures, you should be good. And either way, improvements to RCU's handling of this sort of situation are in the works. And rcutorture has gained tests of this stuff in the last year or so as well, see its "fwd_progress" module parameter and the related code. Thanx, Paul