From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3B8A2CA601D for ; Fri, 9 Oct 2026 10:07:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Nmcl3acLOdghIcVWJGQcNUT1dxt+y4UDcmDoxuevzy8=; b=pe5y5hS+6Knt+DFJAlMSqWHxbK qpH4UiDk634YLEl1MELj8rM4hZjxUssQVAU4UM5bqj+Lq+7C4JDBDw/dQrykdqtgX1vaB7YbSuH4E v7YjdLCYFSTAw/Fm7O4CHuEkmuvCEK2hZ3OvKwLpZRIrhhuYNmS4CJ8Kq8368tJ3pdyCI4VMJpGyE ifzywmd+zd+lWAYhWyiLdkqM86q3kFfk+BeuFRTYFAK0QwREvBD8SURUkRs3iOI3Z/jc59aIaK4nx 7LPOsgy3I0H4KocQ3EHHZFxxABFm6VD7hxXWc9DkK+njHt/CrUhgrISdCYtclsf7KPdLdGi2GfjmH w9CUKIgA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xF7W5-00000005ypa-103m; Fri, 09 Oct 2026 10:07:53 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xF7W4-00000005yox-0cjg for linux-arm-kernel@lists.infradead.org; Fri, 09 Oct 2026 10:07:52 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 30F1A60DBD; Fri, 9 Oct 2026 10:07:51 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A92A41F00893; Fri, 9 Oct 2026 10:07:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791540470; bh=Nmcl3acLOdghIcVWJGQcNUT1dxt+y4UDcmDoxuevzy8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=KOQvmO+cNIRV/YyuucnkVz9UG5LzNGDqnaVyRUMTsdkrXSJ8Fmzny2YgV2PDIB6+m 0uWHPbFLAEtjvO9ZBI14iLjFnyycNHnPy9IBDCUZtTR9t+DC3r8tpZwUm8NSgOPkNU HPhj/vecc6HUAprhbE394HHGweNe+YxrdyhmvM8CAJjOzHscZZQ5IyCj/OHQX/KLed DAdR8KXvnhgw0ssXcFwYVzh3eYwxbQStAR+GWKNLAUpWJjiqqIpfgDYz7JSrmK8Rb+ nYXjdXqaWwKNf7Pa+3ELyzZbOkVw9mXAGMZJ2S2LE2UaPWc5DJf13IUtl3Zzbkt5df LjldAEUGNy8pg== From: Will Deacon To: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, Will Deacon , Thomas Gleixner , Ben Horgan , =?UTF-8?q?=C8=98tefania=20Ion?= , Catalin Marinas , Pankaj Patil , Borislav Petkov , Lorenzo Pieralisi , Jinjie Ruan , Mark Rutland , Tarun Sahu , Fuad Tabba , David Woodhouse , Peter Zijlstra , Marc Zyngier Subject: [PATCH v2 01/23] cpu/hotplug: Clean up cmpxchg() logic in cpuhp_can_boot_ap() Date: Fri, 9 Oct 2026 11:07:12 +0100 Message-ID: <20261009100738.31288-2-will@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261009100738.31288-1-will@kernel.org> References: <20261009100738.31288-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org cpuhp_can_boot_ap() uses atomic_try_cmpxchg() to transition the sync state of the incoming CPU to SYNC_STATE_KICKED. However, this is unnecessary if the state is SYNC_STATE_DEAD, since there will not be any concurrent state modifications, and also if the state is already set to SYNC_STATE_KICKED. Restrict the use of cmpxchg() to the case where the existing state is SYNC_STATE_ALIVE. Reviewed-by: Jinjie Ruan Signed-off-by: Will Deacon --- kernel/cpu.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index b3c8553d7bd6..198c929c452a 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -408,22 +408,22 @@ static bool cpuhp_can_boot_ap(unsigned int cpu) switch (sync) { case SYNC_STATE_DEAD: /* CPU is properly dead */ + atomic_set(st, SYNC_STATE_KICKED); break; case SYNC_STATE_KICKED: /* CPU did not come up in previous attempt */ break; case SYNC_STATE_ALIVE: /* CPU is stuck cpuhp_ap_sync_alive(). */ + if (!atomic_try_cmpxchg_relaxed(st, &sync, SYNC_STATE_KICKED)) + goto again; break; default: /* CPU failed to report online or dead and is in limbo state. */ return false; } - /* Prepare for booting */ - if (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_KICKED)) - goto again; - + /* Continue with booting */ return true; } -- 2.56.0.385.gd3acb90ef8-goog