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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: <1529484440-20634-1-git-send-email-byungchul.park@lge.com> <1529484440-20634-2-git-send-email-byungchul.park@lge.com> <20180620145814.GQ3593@linux.vnet.ibm.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180622143247.781028b1@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18062220-0060-0000-0000-0000028152A9 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009242; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000265; SDB=6.01050834; UDB=6.00538565; IPR=6.00829804; MB=3.00021811; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-22 20:57:01 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062220-0061-0000-0000-0000458ADFFA Message-Id: <20180622205859.GW3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-22_03:,, 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=8.0.1-1806210000 definitions=main-1806220230 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 02:32:47PM -0400, Steven Rostedt wrote: > On Fri, 22 Jun 2018 11:19:16 -0700 > Joel Fernandes wrote: > > > Sure. So in a later thread you mentioned "usermode helpers". I took a closer > > look at that subsystem, and it seems you can execute usermode helpers from > > atomic sections with help of UMH_NO_WAIT flag. > > > > Then I checked where this flag is used and it turns out its from the > > mce_work_trigger function in x86/kernel/cpu/mcheck/dev-mcelog.c which can be > > called infact from an interrupt context (mce_notify_irq). > > > > Is this the usecase you remember causing this weird transitions to userspace? > > But this case still looks like it uses work queues, it just doesn't > wait for the result. > > I'll have to look at the code from what it looked like back in 2011, to > see if there was an actual issue here back then. There was. Been there, got the failure on real hardware. ;-) Thanx, Paul