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[103.168.172.200]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4750804b8c7sm9593281cf.33.2025.03.04.19.05.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Mar 2025 19:05:17 -0800 (PST) Received: from phl-compute-12.internal (phl-compute-12.phl.internal [10.202.2.52]) by mailfauth.phl.internal (Postfix) with ESMTP id 692DB120006A; Tue, 4 Mar 2025 22:05:16 -0500 (EST) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-12.internal (MEProxy); Tue, 04 Mar 2025 22:05:16 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefvddrtddtgddutdefjeefucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdggtfgfnhhsuhgsshgtrhhisggv pdfurfetoffkrfgpnffqhgenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpih gvnhhtshculddquddttddmnecujfgurhephffvvefufffkofgjfhgggfestdekredtredt tdenucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrih hlrdgtohhmqeenucggtffrrghtthgvrhhnpeegleejiedthedvheeggfejveefjeejkefg veffieeujefhueeigfegueehgeeggfenucevlhhushhtvghrufhiiigvpedtnecurfgrrh grmhepmhgrihhlfhhrohhmpegsohhquhhnodhmvghsmhhtphgruhhthhhpvghrshhonhgr lhhithihqdeiledvgeehtdeigedqudejjeekheehhedvqdgsohhquhhnrdhfvghngheppe hgmhgrihhlrdgtohhmsehfihigmhgvrdhnrghmvgdpnhgspghrtghpthhtohepfeekpdhm ohguvgepshhmthhpohhuthdprhgtphhtthhopehrtghusehvghgvrhdrkhgvrhhnvghlrd horhhgpdhrtghpthhtohepphhmlhgruggvkhesshhushgvrdgtohhmpdhrtghpthhtohep rhhoshhtvgguthesghhoohgumhhishdrohhrghdprhgtphhtthhopehjohhhnhdrohhgnh gvshhssehlihhnuhhtrhhonhhigidruggvpdhrtghpthhtohepshgvnhhoiihhrghtshhk hiestghhrhhomhhiuhhmrdhorhhgpdhrtghpthhtohepphgruhhlmhgtkheskhgvrhhnvg hlrdhorhhgpdhrtghpthhtohepfhhrvgguvghrihgtsehkvghrnhgvlhdrohhrghdprhgt phhtthhopehnvggvrhgrjhdruhhprgguhhihrgihsehkvghrnhgvlhdrohhrghdprhgtph htthhopehjohgvlhesjhhovghlfhgvrhhnrghnuggvshdrohhrgh X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 4 Mar 2025 22:05:15 -0500 (EST) From: Boqun Feng To: rcu@vger.kernel.org Cc: Petr Mladek , Steven Rostedt , John Ogness , Sergey Senozhatsky , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Davidlohr Bueso , Shuah Khan , Sebastian Andrzej Siewior , Clark Williams , Masami Hiramatsu , Yuntao Wang , Andrew Morton , Rasmus Villemoes , Guo Weikang , KP Singh , Huang Shijie , Raul E Rangel , Joel Granados , Anna Schumaker , "Martin K. Petersen" , =?utf-8?q?Thomas_Wei?= =?utf-8?q?=C3=9Fschuh?= , zhangguopeng , Thomas Gleixner , "Neeraj Upadhyay (AMD)" , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rt-devel@lists.linux.dev, Zilin Guan Subject: [PATCH rcu 02/10] rcu: Remove READ_ONCE() for rdp->gpwrap access in __note_gp_changes() Date: Tue, 4 Mar 2025 19:04:57 -0800 Message-ID: <20250305030505.94059-3-boqun.feng@gmail.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250305030505.94059-1-boqun.feng@gmail.com> References: <20250305030505.94059-1-boqun.feng@gmail.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Zilin Guan There is one access to the per-CPU rdp->gpwrap field in the __note_gp_changes() function that does not use READ_ONCE(), but all other accesses do use READ_ONCE(). When using the 8*TREE03 and CONFIG_NR_CPUS=8 configuration, KCSAN found no data races at that point. This is because all calls to __note_gp_changes() hold rnp->lock, which excludes writes to the rdp->gpwrap fields for all CPUs associated with that same leaf rcu_node structure. This commit therefore removes READ_ONCE() from rdp->gpwrap accesses within the __note_gp_changes() function. Signed-off-by: Zilin Guan Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng --- kernel/rcu/tree.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 475f31deed14..e4c0ce600b2b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1254,7 +1254,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) /* Handle the ends of any preceding grace periods first. */ if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) || - unlikely(READ_ONCE(rdp->gpwrap))) { + unlikely(rdp->gpwrap)) { if (!offloaded) ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */ rdp->core_needs_qs = false; @@ -1268,7 +1268,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) /* Now handle the beginnings of any new-to-this-CPU grace periods. */ if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) || - unlikely(READ_ONCE(rdp->gpwrap))) { + unlikely(rdp->gpwrap)) { /* * If the current grace period is waiting for this CPU, * set up to detect a quiescent state, otherwise don't @@ -1283,7 +1283,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); - if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap)) + if (IS_ENABLED(CONFIG_PROVE_RCU) && rdp->gpwrap) WRITE_ONCE(rdp->last_sched_clock, jiffies); WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp);