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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Sun, 1 Jul 2018 23:01:02 -0400 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 w62311UL18743598 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 2 Jul 2018 03:01:01 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BB872B2066; Sun, 1 Jul 2018 23:00:47 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A38A9B2072; Sun, 1 Jul 2018 23:00:47 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.80.206.224]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Sun, 1 Jul 2018 23:00:47 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 45A7C16CA314; Sun, 1 Jul 2018 20:03:13 -0700 (PDT) Date: Sun, 1 Jul 2018 20:03:13 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com Subject: Re: [PATCH RFC tip/core/rcu 1/2] rcu: Defer reporting RCU-preempt quiescent states when disabled Reply-To: paulmck@linux.vnet.ibm.com References: <20180627204835.GA25456@linux.vnet.ibm.com> <20180627204915.27253-1-paulmck@linux.vnet.ibm.com> <20180701174045.GA111992@joelaf.mtv.corp.google.com> <20180701222501.GC3593@linux.vnet.ibm.com> <20180702003732.GB95395@joelaf.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180702003732.GB95395@joelaf.mtv.corp.google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18070203-0072-0000-0000-000003781DED X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009292; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01055266; UDB=6.00541227; IPR=6.00833188; MB=3.00021955; MTD=3.00000008; XFM=3.00000015; UTC=2018-07-02 03:01:06 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18070203-0073-0000-0000-0000488ED626 Message-Id: <20180702030313.GH3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-07-01_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=8.0.1-1806210000 definitions=main-1807020034 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 01, 2018 at 05:37:32PM -0700, Joel Fernandes wrote: > On Sun, Jul 01, 2018 at 03:25:01PM -0700, Paul E. McKenney wrote: > [...] > > > > @@ -602,6 +589,66 @@ static void rcu_read_unlock_special(struct task_struct *t) > > > > } > > > > } > > > > > > > > +/* > > > > + * Is a deferred quiescent-state pending, and are we also not in > > > > + * an RCU read-side critical section? It is the caller's responsibility > > > > + * to ensure it is otherwise safe to report any deferred quiescent > > > > + * states. The reason for this is that it is safe to report a > > > > + * quiescent state during context switch even though preemption > > > > + * is disabled. This function cannot be expected to understand these > > > > + * nuances, so the caller must handle them. > > > > + */ > > > > +static bool rcu_preempt_need_deferred_qs(struct task_struct *t) > > > > +{ > > > > + return (this_cpu_ptr(&rcu_preempt_data)->deferred_qs || > > > > + READ_ONCE(t->rcu_read_unlock_special.s)) && > > > > + !t->rcu_read_lock_nesting; > > > > +} > > > > + > > > > +/* > > > > + * Report a deferred quiescent state if needed and safe to do so. > > > > + * As with rcu_preempt_need_deferred_qs(), "safe" involves only > > > > + * not being in an RCU read-side critical section. The caller must > > > > + * evaluate safety in terms of interrupt, softirq, and preemption > > > > + * disabling. > > > > + */ > > > > +static void rcu_preempt_deferred_qs(struct task_struct *t) > > > > +{ > > > > + unsigned long flags; > > > > + > > > > + if (!rcu_preempt_need_deferred_qs(t)) > > > > + return; > > > > + local_irq_save(flags); > > > > + rcu_preempt_deferred_qs_irqrestore(t, flags); > > > > +} > > > > + > > > > +/* > > > > + * Handle special cases during rcu_read_unlock(), such as needing to > > > > + * notify RCU core processing or task having blocked during the RCU > > > > + * read-side critical section. > > > > + */ > > > > +static void rcu_read_unlock_special(struct task_struct *t) > > > > +{ > > > > + unsigned long flags; > > > > + bool preempt_bh_were_disabled = !!(preempt_count() & ~HARDIRQ_MASK); > > > > > > Would it be better to just test for those bits just to be safe the higher > > > order bits don't bleed in, such as PREEMPT_NEED_RESCHED, something like the > > > following based on the 'dev' branch? > > > > Good point! My plan is to merge it into the original commit with > > attribution. Please let me know if you have objections. > > > > Sure! That sounds good to me. Very good, I now have a "squash" commit queued, thank you! Thanx, Paul