From patchwork Wed Oct 9 18:00:45 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13828941 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 62F401E133D; Wed, 9 Oct 2024 18:00:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728496847; cv=none; b=e2FOnXyXXvLJKAGKGxDPeJXqA0rNFXBxzadbVf/FqB+soKdM3p4JV73IQTFDhKJJXKYcRyXQq8THvYDX3wgFkzMN/4G4JZ8SUFVe7Sa54nvjwRFanKPgnQvXZ2c+U6o+JiyNnJad221vwBZ/uCrRk+/go6qPoJTHKt6FofvbsM8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728496847; c=relaxed/simple; bh=BE0VZPoXza7bZDtTDVSPUqFCnHF2OgmKDYBLxOWLPvQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=uhEMFH/9Q3KPnTlJQ9cY9CKt5Q/PO+StT1JzU1nep8U8NhounOoEUow2AxNUq4ZAw9tojNCXGqqsETQ9xJz7gXDkhWamrRfNscmTxHoE8FU8fcAKbcL/JXHbm4FZXKntG5GUWxfRGOVa2bJnUMhfv7Vs2PrimhQkv8DFiA6kA88= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cSgb6JLC; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cSgb6JLC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2241FC4CED7; Wed, 9 Oct 2024 18:00:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728496847; bh=BE0VZPoXza7bZDtTDVSPUqFCnHF2OgmKDYBLxOWLPvQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cSgb6JLCD6/eZ6VcL/J+ttiZoKnA5InYMWxGf6IZNG58AcF56ux1pTX+3yxV0ETPm mAMIJyl5Vn3EIprs4C5J27iNr1aQGVFo/pFLTkW//STjNPDAl0w0Eaiu4FR/UfBg4k n673YC9AU7ubzxYb+cy7MHGwy8kTpR3HMgNEFpYozYuTRJZfIGZXsnny6rPvtsITGq on3guSxt3/Y3UC6wXnA6GqVEcdudq0N2sJxBHRzxt3UEO16gS73IZgartBEjypvBqI AHCd/xZJNtNmO14X/nWysa+8krybY+HOZfJajf/OpnBghzZBgdVHLcJmZJcrL2rri2 LQ5VGRda2LrnA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 790CCCE1290; Wed, 9 Oct 2024 11:00:46 -0700 (PDT) From: "Paul E. McKenney" To: frederic@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH rcu 7/7] rcu-tasks: Remove open-coded one-byte cmpxchg() emulation Date: Wed, 9 Oct 2024 11:00:45 -0700 Message-Id: <20241009180045.777721-7-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <2dc6de07-374d-44da-82e9-fa9d9c516b46@paulmck-laptop> References: <2dc6de07-374d-44da-82e9-fa9d9c516b46@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 This commit removes the open-coded one-byte cmpxchg() emulation from rcu_trc_cmpxchg_need_qs(), replacing it with just cmpxchg() given the latter's new-found ability to handle single-byte arguments across all architectures. Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 17 +---------------- 1 file changed, 1 insertion(+), 16 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index dd9730fd44fbe..c789d994e7ebc 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1541,22 +1541,7 @@ static void rcu_st_need_qs(struct task_struct *t, u8 v) */ u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new) { - union rcu_special ret; - union rcu_special trs_old = READ_ONCE(t->trc_reader_special); - union rcu_special trs_new = trs_old; - - if (trs_old.b.need_qs != old) - return trs_old.b.need_qs; - trs_new.b.need_qs = new; - - // Although cmpxchg() appears to KCSAN to update all four bytes, - // only the .b.need_qs byte actually changes. - instrument_atomic_read_write(&t->trc_reader_special.b.need_qs, - sizeof(t->trc_reader_special.b.need_qs)); - // Avoid false-positive KCSAN failures. - ret.s = data_race(cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s)); - - return ret.b.need_qs; + return cmpxchg(&t->trc_reader_special.b.need_qs, old, new); } EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs);