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 36BF134CFB9 for ; Fri, 9 Oct 2026 10:07:51 +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=1791540472; cv=none; b=f8iEAxTqOWnHUPiwCZ7Y1vr8Of/aee+/c+2YWWp5eG26Zmk3BfyAl0xwtpBanN4bL6SXhypi27oYxRFtvBOtOgXw/nkpjHESLHckB/96qdAXqWcNpvOsZWDc0s4Iq60phnl7ji491jXNArBPdacD6Jj7Ado1aJ/50zuQuZAvhc8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791540472; c=relaxed/simple; bh=Rq/kuDq+rDL8Cxo8P2KFv74mO08o1Bg5PK9tRs/+gN8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZueGbGJgJSGzd6aleHVoIcZ4gmy4g577gYLYeNP9P/XLyaMSaMJebpYu69tBiaqk2Aae+1d1vDvCc6XrIApu9heJKYeF8rQXmOTnrfse/fz+fL4ipLrfmYQ4IbO30/zXeEogNLZyEydVXY9G4sakrnBhEeXnIkArFbllcmLaizk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KOQvmO+c; 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="KOQvmO+c" 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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