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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53977C433EF for ; Mon, 9 May 2022 13:59:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236686AbiEIODo (ORCPT ); Mon, 9 May 2022 10:03:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57556 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236626AbiEIODg (ORCPT ); Mon, 9 May 2022 10:03:36 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CEB9716D5CC for ; Mon, 9 May 2022 06:59:42 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1652104781; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FDSynU42H0ANPTpjgbswkYJXVZufPOPf8nzkhHqjA9g=; b=vmKUlABhaBvEYz0X9LA3g5SRs3q6NK9pjEq5HDfdrkv8DNhJiu+xhSkMA6zdgQEprlDzCg uQWR46Hiz1n5Y0hzLAPihWXSh1PrxlSYk2hsuQTYX1OFGec+wVrZGK7qp4we6RqTX+Qakh BSagp92ogKOfiZ4quMyZMILbTxMIr02LfddqQvQLeX/k6xcU1kjTJJJN9L3wNd+67mHM8m 16UrGlt5n8Yz3RlqdYJT1GHL7F4HJ3T/aHL+iOWbDqGgRE84ihDkeISbp4UTxCINqutLyz 0i120YG1QFJBnP0HMncXXV9Af4R86Xe56Ls8BflDNQUL6C1XIO8Zsz+kiLneKg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1652104781; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FDSynU42H0ANPTpjgbswkYJXVZufPOPf8nzkhHqjA9g=; b=VlTE3d1mTqdZW3KhBs4KorVfZhqO0/Xdh68Ua4w6Qxm6hC/qsLC7dU9afDjI28gB3NaJhD xlvkhK2X24Pr7XCw== To: Ricardo Neri , x86@kernel.org Cc: Tony Luck , Andi Kleen , Stephane Eranian , Andrew Morton , Joerg Roedel , Suravee Suthikulpanit , David Woodhouse , Lu Baolu , Nicholas Piggin , "Ravi V. Shankar" , Ricardo Neri , iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Ricardo Neri Subject: Re: [PATCH v6 21/29] x86/nmi: Add an NMI_WATCHDOG NMI handler category In-Reply-To: <20220506000008.30892-22-ricardo.neri-calderon@linux.intel.com> References: <20220506000008.30892-1-ricardo.neri-calderon@linux.intel.com> <20220506000008.30892-22-ricardo.neri-calderon@linux.intel.com> Date: Mon, 09 May 2022 15:59:40 +0200 Message-ID: <87a6bqrelv.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 05 2022 at 17:00, Ricardo Neri wrote: > Add a NMI_WATCHDOG as a new category of NMI handler. This new category > is to be used with the HPET-based hardlockup detector. This detector > does not have a direct way of checking if the HPET timer is the source of > the NMI. Instead, it indirectly estimates it using the time-stamp counter. > > Therefore, we may have false-positives in case another NMI occurs within > the estimated time window. For this reason, we want the handler of the > detector to be called after all the NMI_LOCAL handlers. A simple way > of achieving this with a new NMI handler category. > > @@ -379,6 +385,10 @@ static noinstr void default_do_nmi(struct pt_regs *regs) > } > raw_spin_unlock(&nmi_reason_lock); > > + handled = nmi_handle(NMI_WATCHDOG, regs); > + if (handled == NMI_HANDLED) > + goto out; > + How is this supposed to work reliably? If perf is active and the HPET NMI and the perf NMI come in around the same time, then nmi_handle(LOCAL) can swallow the NMI and the watchdog won't be checked. Because MSI is strictly edge and the message is only sent once, this can result in a stale watchdog, no? Thanks, tglx