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McKenney" To: Sebastian Andrzej Siewior Cc: tglx@linutronix.de, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: rcu: Merge RCU-bh into RCU-preempt Reply-To: paulmck@linux.ibm.com References: <20181101231804.GA11280@linux.ibm.com> <20181108160256.xpawe65h5lm65soi@linutronix.de> <20181108164247.GL4170@linux.ibm.com> <20181108171516.axwvjtgay4zolc56@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181108171516.axwvjtgay4zolc56@linutronix.de> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18110817-0052-0000-0000-00000352BE3E X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010008; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000269; SDB=6.01114540; UDB=6.00577845; IPR=6.00894638; MB=3.00024077; MTD=3.00000008; XFM=3.00000015; UTC=2018-11-08 17:35:27 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18110817-0053-0000-0000-00005EB31127 Message-Id: <20181108173525.GO4170@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-08_08:,, 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=8.0.1-1807170000 definitions=main-1811080148 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 08, 2018 at 06:15:16PM +0100, Sebastian Andrzej Siewior wrote: > On 2018-11-08 08:42:47 [-0800], Paul E. McKenney wrote: > > On Thu, Nov 08, 2018 at 05:02:57PM +0100, Sebastian Andrzej Siewior wrote: > > > On 2018-11-01 16:18:04 [-0700], Paul E. McKenney wrote: > > > > The need for this goes away as of the current merge window because > > > > RCU-bh has gone away. (Aside from still being able to do things > > > > like rcu_read_lock_bh() as a documentation device.) > > > > > > So in -RT rcu_read_lock_bh() does > > > { local_bh_disable() ; rcu_read_lock() } > > > > > > So you are saying that this is also the case in v4.20? > > > > No, rcu_read_lock_bh() and rcu_read_unlock_bh() are unchanged in v4.20. > > With the new RCU grace-period mechanism, local_bh_disable() blocks future > > grace periods on its own. > > > > Unless I am missing something (quite probable, actually), the v4.20 > > definitions of rcu_read_lock_bh() and rcu_read_unlock_bh() should work > > as-is for -rt. > > I *think* tglx made this patch, then you somehow reverted it partly [0] > and the final piece we need for RT is this gem: > > https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/patches/rcu-Eliminate-softirq-processing-from-rcutree.patch?h=linux-4.19.y-rt-patches > > [0] rcu: Make ksoftirqd do RCU quiescent states > https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/patches/patch-to-introduce-rcu-bh-qs-where-safe-from-softirq.patch?h=linux-4.19.y-rt-patches I agree that tglx's patch is needed for 4.19 and earlier. Just not for 4.20 and later. Or am I still missing your point? Thanx, Paul