From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 474D12DEA6B; Fri, 31 Jul 2026 01:01:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785459717; cv=none; b=ozowrpQ6aiSwys9SBm1ysAIOKxUMV9s+pjIahhxjiaviyNxRHQvgnLsbJmDyLUkevjLy/FixH2shXxjIcwY4DX3YuN3N+7EUAwGOzT5d5+dVi4qIcShbdzKTaZMPsIRVN4AV22SqoFvydZPTDIuYH2PPJDdZCpw6zz5OKf8yY14= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785459717; c=relaxed/simple; bh=SPQ1/BUBlVcPW0YL9pl+7LJ6fudss7Cc5flDcSz3Cxg=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=FHmx3gN014Yq6UlGxRME8hdkfWMOvjqmv6/gAzvXGROoCVD92xtgKtSTTbttodH/EORNZJSAFnK3K6tsVpdGRuZjvhjWL/Tna0E0rSCDWsRd9Sw0ofPC9GuZSbijBHCPp8EqHIcTmqFrc6zbVm6HFWC41Aq/hrfJRUrVllAav/M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Bprqa4Ub; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Bprqa4Ub" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B14F1F00ACF; Fri, 31 Jul 2026 01:01:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785459715; bh=w3yDZIsaofBYHwPlrh6CqR5JrMhsol0jdD2BGuIKVOc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Bprqa4Ub3Pu39FxWUhvluMpCYw6kwP6Rpdzoz1SuEDYCPdQYXIC6OSJug+5TheC6M OsycQ9Dd6DtkitMZgy7YJXXuMcz0RtGG6B9PSbSPDZuTMeSHLxuyvoYr7hLjnUrtEP r4KKcA4/ZXbmHxO58VI2kW6E1eBKPkwpxk0cmspavcTcgt5IWOCx1ARl5ZFk8YmeI5 Iw5lG58H9djj0ZNQSvgqqKCne6GjLGK1M1KwIfIO/BMvvQsUTPN6ndekzRaqp2gRso RbufSTtPMqQKkn4Mci2ZZ3e50GBlHhTSF5oFA25VkVlUB/PN+JyfLbikO7Wj+cQa+4 tQkR+twwjNpJg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id B5242CE1497; Thu, 30 Jul 2026 18:01:54 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH RFC 08/16] rcu: Use WRITE_ONCE() for ->rcu_need_heavy_qs Date: Thu, 30 Jul 2026 18:01:45 -0700 Message-Id: <20260731010153.3531313-8-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <9de287bc-e565-4f21-bd3c-5c17792e6abc@paulmck-laptop> References: <9de287bc-e565-4f21-bd3c-5c17792e6abc@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Currently raw_cpu_write() is used to clear the ->rcu_need_heavy_qs field of the per-CPU rcu_data structure. However, on x86 this is a normal assignment, which does not play well with concurrent accesses. This commit therefore upgrades the uses of raw_cpu_write() to its concurrency-safe counterpart WRITE_ONCE() of an rdp pointer obtained from this_cpu_ptr(&rcu_data). KCSAN located this issue. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 03a43d3d261607..91d5b4dd08bf5c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -357,9 +357,10 @@ bool rcu_watching_zero_in_eqs(int cpu, int *vp) */ notrace void rcu_momentary_eqs(void) { + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); int seq; - raw_cpu_write(rcu_data.rcu_need_heavy_qs, false); + WRITE_ONCE(rdp->rcu_need_heavy_qs, false); seq = ct_state_inc(2 * CT_RCU_WATCHING); /* It is illegal to call this from idle state. */ WARN_ON_ONCE(!(seq & CT_RCU_WATCHING)); -- 2.40.1