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Fri, 13 Mar 2026 09:39:37 +0000 (GMT) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Fri, 13 Mar 2026 10:39:37 +0100 From: Harald Freudenberger To: Heiko Carstens Cc: lirongqing , Holger Dengler , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , linux-s390@vger.kernel.org Subject: Re: [PATCH] s390/pkey: Remove synchronize_rcu from pkey_handler_register Reply-To: freude@linux.ibm.com Mail-Reply-To: freude@linux.ibm.com In-Reply-To: <20260313090641.13729Aae-hca@linux.ibm.com> References: <20260313052312.2389-1-lirongqing@baidu.com> <058c161c4e82d2d78ddb9c52cfc8ee50@linux.ibm.com> <20260313090641.13729Aae-hca@linux.ibm.com> Message-ID: X-Sender: freude@linux.ibm.com Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=QKtlhwLL c=1 sm=1 tr=0 ts=69b3db5c cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=kj9zAlcOel0A:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=zuLzuavZAAAA:8 a=VnNF1IyMAAAA:8 a=69zs-H1v8mSJLVq8d6sA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzEzMDA2OSBTYWx0ZWRfX59y93FRDLBj3 3DN50aOsEwnBhdNY/iRu+kZr8cRv4oFB4jRlnRItwhIk5ujfPB6VJ4izq6S371Wir+aac3cazbj s/pp5iP28Wz201hDaa24dIhsuwVjTEl2mSc+8OI1sD4JeJaCDQaLsBo3K8BKlCiVNz8chyI1nHr IE7WdyR4PpnjI1bPK1s+aUdZ5LYHpYm2JP0CBxQ7Ydc8tMvwk/i+2OkU3GVZRWFEuBV5CZgfhI0 9ll/gEmUqB8I8xhiJGudy4Ke6DKLUHamqG2LMZftfwBM8dJiGF93pkcRVAF/Bt0NjEkYAV7T7/i qktyAqaWSSXuH3PPkxiJ+CQMCVPPCmO/TDPpD0UTr1eLT8e7ol4/mwM3gmYKZa5Ln15mCm9wYZN oI21WOMvyP1o9aLvif24WSNUFRvtQBRQg7iVVc1pW9yXJ8DzkfLIrEW3B3l/abTfdLwm1f/NOTw 9uohjhZlcUgCUpjAwzg== X-Proofpoint-ORIG-GUID: swXUrimCMpKN8rMB4hmnPMvq53pyY4Te X-Proofpoint-GUID: swXUrimCMpKN8rMB4hmnPMvq53pyY4Te X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-13_01,2026-03-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 impostorscore=0 clxscore=1015 priorityscore=1501 bulkscore=0 adultscore=0 phishscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603130069 On 2026-03-13 10:06, Heiko Carstens wrote: > On Fri, Mar 13, 2026 at 09:32:39AM +0100, Harald Freudenberger wrote: >> On 2026-03-13 06:23, lirongqing wrote: >> > From: Li RongQing >> > >> > The synchronize_rcu() call after adding a handler to the handler_list >> > is redundant because RCU readers will either see the old list or the >> > new list. Removing this synchronization point reduces the blocking >> > time during handler registration. >> > >> > Signed-off-by: Li RongQing >> > --- >> > drivers/s390/crypto/pkey_base.c | 1 - >> > 1 file changed, 1 deletion(-) >> > >> > diff --git a/drivers/s390/crypto/pkey_base.c >> > b/drivers/s390/crypto/pkey_base.c >> > index d60cd98..c2e29d6 100644 >> > --- a/drivers/s390/crypto/pkey_base.c >> > +++ b/drivers/s390/crypto/pkey_base.c >> > @@ -60,7 +60,6 @@ int pkey_handler_register(struct pkey_handler >> > *handler) >> > >> > list_add_rcu(&handler->list, &handler_list); >> > spin_unlock(&handler_list_write_lock); >> > - synchronize_rcu(); >> > >> > module_put(handler->module); >> >> Thanks Li RongQing >> >> Reviewed-by: Harald Freudenberger > > With synchronize_rcu() you do know that other CPUs will see the new > list after this function returned, without not. Is that ok? No - If this has side effects then I'll discuss this with you and then may also run some tests - so please hold back until I'll give a green light on this. Thanks for this hint.