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McKenney" To: Steven Rostedt Cc: Byungchul Park , jiangshanlai@gmail.com, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, kernel-team@lge.com, joel@joelfernandes.org Subject: Re: [RFC 1/2] rcu: Do prepare and cleanup idle depending on in_nmi() Reply-To: paulmck@linux.vnet.ibm.com References: <1529484440-20634-1-git-send-email-byungchul.park@lge.com> <20180620145058.GP3593@linux.vnet.ibm.com> <20180620114335.7a314642@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180620114335.7a314642@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18062015-2213-0000-0000-000002BCBBFA X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009227; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000265; SDB=6.01049774; UDB=6.00537929; IPR=6.00828746; MB=3.00021761; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-20 15:55:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062015-2214-0000-0000-00005A8C0D12 Message-Id: <20180620155658.GU3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-20_07:,, 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=8.0.1-1805220000 definitions=main-1806200174 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 20, 2018 at 11:43:35AM -0400, Steven Rostedt wrote: > On Wed, 20 Jun 2018 07:50:58 -0700 > "Paul E. McKenney" wrote: > > > On Wed, Jun 20, 2018 at 05:47:19PM +0900, Byungchul Park wrote: > > > Get rid of dependency on ->dynticks_nmi_nesting. > > > > > > Signed-off-by: Byungchul Park > > > --- > > > kernel/rcu/tree.c | 22 ++++++++++------------ > > > 1 file changed, 10 insertions(+), 12 deletions(-) > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index deb2508..59ae94e 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -797,6 +797,11 @@ void rcu_nmi_exit(void) > > > return; > > > } > > > > > > + if (!in_nmi()) { > > > > Is in_nmi() sufficiently reliable for use here? In the past, there have > > been tracepoints that invoked these functions between the time that the > > handlers were entered and the time that software updated the state so that > > the various handler-check functions (such as in_nmi()) would return true. > > > > Steve, has there been any change in this situation? > > There shouldn't be any "trace events", but what we had to deal with was > function tracing. And in the near future, we will be getting "function > based events" that will allow you to create an event in any function. > > That said, even the function tracer shouldn't be called from the time > the NMI triggers to "in_nmi()" is set. Because there's some function > tracer callbacks that should not be executed from an NMI, and I use > in_nmi() to determine if they get called or not. OK, so in theory this change is safe from a tracing perspective. But it does add conditionals to a fastpath. Byungchul, is there any reason to make this change other than preparation for your second patch? Thanx, Paul