From nobody Mon Feb 9 14:31:20 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40933C71153 for ; Mon, 4 Sep 2023 15:23:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350336AbjIDPXL (ORCPT ); Mon, 4 Sep 2023 11:23:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231740AbjIDPXK (ORCPT ); Mon, 4 Sep 2023 11:23:10 -0400 Received: from mail-ej1-x635.google.com (mail-ej1-x635.google.com [IPv6:2a00:1450:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5DF7219A9 for ; Mon, 4 Sep 2023 08:22:44 -0700 (PDT) Received: by mail-ej1-x635.google.com with SMTP id a640c23a62f3a-99bed101b70so243993466b.3 for ; Mon, 04 Sep 2023 08:22:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1693840962; x=1694445762; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=323vdBuxHbzfbTouYgBjNEzO4rAlD1GsQQDDZWD9Blg=; b=DORy+/3sn5yDP8O6ZIjlm3te2ZZmZr8lyDKMhTPo4hQqu/P8EdQ6qZId5ZkG0PcNNq fw/Ua391DXbMsaRM5Vh9rcPt2JA4nYGm7X3fSA9ee0wgPCOwbS21RIRlFMwDrlOlpr7x R6eE769XcHyjiikGqnDwKhRdWBarGAi/q5+MSYue1U06PiLe8NIfBfLAhIGqf9bR0mlL bKybCyT9MJxCbrjKxS/Fu3nDMjQFZcA9XHl3QMYUnW1PnTL2RJOz63mDvtpeQpyhRt1z ySvv0v6TynTohTbYIFSqJ27BrcbDMuxON8tLQN17KhfGqxQlrjU9Ts5wX5wuEdny49i9 AhkQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693840962; x=1694445762; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=323vdBuxHbzfbTouYgBjNEzO4rAlD1GsQQDDZWD9Blg=; b=BvurgxREbLAIAHBOiD42E5lhcz9GvmD+kB5nfWfWrZu0oX+vbqHYxMyDQdmwe0vjk3 tKGS7uIMiVQkmZxJV54mvmCJu6t9szBpXsf0pXQgwGcc6Foo4j/ChR4L3A69SI9aEdAs 54EyX6RVsk2XYG87gjqgkhEny9Uhv9YHbLFb0g5qE7nsZVzkPewNxbeaQINFI3wWyffV FNtc9oDCFhZPtpVmvd82nQybPmsLxR6+z4ke2WD94BpSj0pJbGK1+zo4DOJ22M528g4a 9jQIQEEIHanU6VQziKZdY94fzY+PssdOCF0jIv8duGb0c6/1iJxAut2N9/4gpG0K2tPr hOPg== X-Gm-Message-State: AOJu0Yyu2vOy7BF/DlxKYJYrdNhwYQ5J3Okf87FRJoUE3baAeyLJw+hR oznTrlN1yMSfBKAIbZAk5u1wJqndNPmivQ== X-Google-Smtp-Source: AGHT+IFK4sQFrf6N6lVjyi74AfhL/FMSOqHrsM6TOirMhggEKlkMH99BGqkFUFW/IAvZOLVrETZdvQ== X-Received: by 2002:a17:907:78c2:b0:9a1:b05a:c07c with SMTP id kv2-20020a17090778c200b009a1b05ac07cmr9000209ejc.55.1693840962250; Mon, 04 Sep 2023 08:22:42 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id l13-20020a170906078d00b009a5f1d15642sm6246182ejc.158.2023.09.04.08.22.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Sep 2023 08:22:42 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Andrew Morton Subject: [PATCH] panic: Use atomic_try_cmpxchg in panic() and nmi_panic() Date: Mon, 4 Sep 2023 17:21:01 +0200 Message-ID: <20230904152230.9227-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) =3D=3D old in panic() and nmi_panic(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, rename cpu variable to this_cpu in nmi_panic() and try to unify logic flow between panic() and nmi_panic(). No functional change intended. Cc: Andrew Morton Signed-off-by: Uros Bizjak --- kernel/panic.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/kernel/panic.c b/kernel/panic.c index 07239d4ad81e..8740ac65cb2c 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -192,14 +192,15 @@ atomic_t panic_cpu =3D ATOMIC_INIT(PANIC_CPU_INVALID); */ void nmi_panic(struct pt_regs *regs, const char *msg) { - int old_cpu, cpu; + int old_cpu, this_cpu; =20 - cpu =3D raw_smp_processor_id(); - old_cpu =3D atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu); + old_cpu =3D PANIC_CPU_INVALID; + this_cpu =3D raw_smp_processor_id(); =20 - if (old_cpu =3D=3D PANIC_CPU_INVALID) + /* atomic_try_cmpxchg updates old_cpu on failure */ + if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) panic("%s", msg); - else if (old_cpu !=3D cpu) + else if (old_cpu !=3D this_cpu) nmi_panic_self_stop(regs); } EXPORT_SYMBOL(nmi_panic); @@ -311,15 +312,18 @@ void panic(const char *fmt, ...) * stop themself or will wait until they are stopped by the 1st CPU * with smp_send_stop(). * - * `old_cpu =3D=3D PANIC_CPU_INVALID' means this is the 1st CPU which - * comes here, so go ahead. + * cmpxchg success means this is the 1st CPU which comes here, + * so go ahead. * `old_cpu =3D=3D this_cpu' means we came from nmi_panic() which sets * panic_cpu to this CPU. In this case, this is also the 1st CPU. */ + old_cpu =3D PANIC_CPU_INVALID; this_cpu =3D raw_smp_processor_id(); - old_cpu =3D atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu); =20 - if (old_cpu !=3D PANIC_CPU_INVALID && old_cpu !=3D this_cpu) + /* atomic_try_cmpxchg updates old_cpu on failure */ + if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) + ; + else if (old_cpu !=3D this_cpu) panic_smp_self_stop(); =20 console_verbose(); --=20 2.41.0