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Mon, 16 Mar 2026 09:35:43 +0000 (GMT) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Mon, 16 Mar 2026 10:35:43 +0100 From: Harald Freudenberger To: lirongqing Cc: Holger Dengler , Heiko Carstens , 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: <20260313052312.2389-1-lirongqing@baidu.com> References: <20260313052312.2389-1-lirongqing@baidu.com> Message-ID: <09877680c056890694067390894f2e01@linux.ibm.com> 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-Proofpoint-GUID: rc9LKEmmahRnOglA88wzpDvtu373QlKk X-Proofpoint-ORIG-GUID: rc9LKEmmahRnOglA88wzpDvtu373QlKk X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE2MDA3MCBTYWx0ZWRfX4V7acdQ0rhyX wXWh45a3VO+wDTzFQXlg5GuVmKUChlw277E3C2Q4thWxb296gOlGv2pT7miGMNJsEWxF6sqLGQU j/8DFNtv3zagkqqfAsoI8aT827fuB4W8GdeJ+UBvw1ydHd+nnTiY0WIe5Qu4wUX6xSZRYwQSH55 TD8pqrIJR6V8wWTYC3R1JSj8qr4yNtVewKG4A8Pqt2FKTQ9tPTE3zrRQAjZknSg1sQHGwBmptks 07AbSfvT88ZY7b4IHK5tIzXVfntJmTaYIESKjIhjdIaVd71ejk50SvMnuMGbnqEcB9EsOgl3EY9 +u9wLZkHycjQfSfSf41NDu+5Xu1Q4KkDIRukAUgBdnUvIZFp+SaKfZdQXxhrvTvGYtOnhUUwsO3 LEsF58bxN7PvpJJ94m+mnak6bI/EP8nrKvrpTuu2MlmWbvlMRAnh+AZoGEsLBv1zkVyK3oTc60O oLAlhDtyvYW9/bfuM2Q== X-Authority-Analysis: v=2.4 cv=Hf8ZjyE8 c=1 sm=1 tr=0 ts=69b7cef1 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=kj9zAlcOel0A:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=zuLzuavZAAAA:8 a=lFT4GuY0HqRxgGrVVpkA:9 a=CjuIK1q_8ugA:10 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=2026-03-16_03,2026-03-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 malwarescore=0 lowpriorityscore=0 impostorscore=0 bulkscore=0 suspectscore=0 priorityscore=1501 spamscore=0 adultscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603160070 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); After some deep dive into RCU, and some code review with Holger we decided to leave this statement in the code: This is the fast path to push the info about the updated list to the other cpus. If removed, the other cpus may get the updated list when the RCU context is synched. As this code is in general not performance critical and the list update more or less only occurs at the early time in system startup the focus is on concurrency versus performance. Maybe I'll add a comment onto this code line... Thanks Li RongQing for your patch and suggestions. Harald Freudenberger