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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Sun, 23 Sep 2018 19:55:13 -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 w8NNtCqa14942394 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Sun, 23 Sep 2018 23:55:12 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BD2FAB2068; Sun, 23 Sep 2018 19:53:35 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9E12EB2065; Sun, 23 Sep 2018 19:53:35 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.154.62]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Sun, 23 Sep 2018 19:53:35 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 157E516C1971; Sun, 23 Sep 2018 16:55:12 -0700 (PDT) Date: Sun, 23 Sep 2018 16:55:12 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: LKML Subject: Re: Question about ->head field of rcu_segcblist Reply-To: paulmck@linux.ibm.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18092323-0040-0000-0000-00000474E26A X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009760; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01092701; UDB=6.00564701; IPR=6.00872736; MB=3.00023472; MTD=3.00000008; XFM=3.00000015; UTC=2018-09-23 23:55:14 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18092323-0041-0000-0000-0000087CE565 Message-Id: <20180923235512.GB4222@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-09-23_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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1809230253 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 23, 2018 at 07:31:37PM -0400, Joel Fernandes wrote: > On Sun, Sep 23, 2018 at 7:30 PM Joel Fernandes wrote: > > > > Hi Paul, > > > > I was parsing the Data-Structures document and had a question about > > the following "Important note" text. > > > > Could it be clarified in the below text better why "remaining > > callbacks are placed back on the RCU_DONE_TAIL segment", is a reason > > for not depending on ->head for determining if no callbacks are > > associated with the rcu_segcblist? If callbacks are added back to the > > DONE_TAIL segment, then I would think rcu_head should be != NULL. > > Infact the "rsclp->head = *rsclp->tails[RCU_DONE_TAIL];" in > > rcu_segcblist_extract_done_cbs should set the ->head to NULL if I > > understand correctly. > > Just to clarify, I meant set to NULL assuming all cbs were done > waiting and ready to be invoked. Ah, good, then that is correct. But even then, being NULL doesn't mean no callbacks because they might be temporarily held by rcu_do_batch(). Thanx, Paul