From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 405CD31A89 for ; Thu, 5 Sep 2024 03:23:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725506614; cv=none; b=oQwt8KXELAiKpDALvySuaQ7khAAWLw5kwgCXIFYblY4NfxX6sTMOkBxFoW/UsKlS5X6EoT0S+ye9y7F8hDM/y8lMSKMwVYTDi54ZPPB3h+IeFoltejN1AvqSjB4iZVsrG65x2oFX5ibHSmUftkDdNeH5I3CNvMCLS0rLU91sVR8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725506614; c=relaxed/simple; bh=5AaEcoNV9j1SRoWP/YiH9so7VP+RnZlAxDet4kTONbo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=azyeo75aK7RlRlfnnpc9KVOOCC0AJD9h3N5etWappI4VJWVOhHudFAkgxlESqZxlcQIGE0Wc4ihUEDGYvgs4LyQIvUjEmBoilRTz4uAlz6NV/W+95+rdzj/zp2SF+ci38mqt1f7dJ+AFefNNQLjg/a2MRu9fZTptqn8NpVnn+HA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=C4OUNgPW; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="C4OUNgPW" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725506610; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HTNSGL25zCLG+PtyocxhqR9poI911nBZG+X7qZt1q6o=; b=C4OUNgPWvE5a8RSX3ZZtaXPPa4AhPWY2M1Lo1rq3CN9wYESFxhXctvBWC5obMRUt8JmDYB eIlF86w8R4R3fFVaYX8bpbfVTuAVSGl/IxtZh4bHpjMT2Jrne/rZJ36qjBxFK8270WfrN0 W+E334jK84PItpJypxT8tSnYWocdUno= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-260-xc-9i_YyNRWBh0VIswKbpA-1; Wed, 04 Sep 2024 23:23:25 -0400 X-MC-Unique: xc-9i_YyNRWBh0VIswKbpA-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 884571977021; Thu, 5 Sep 2024 03:23:21 +0000 (UTC) Received: from localhost (unknown [10.72.112.58]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3C7A41955D53; Thu, 5 Sep 2024 03:23:18 +0000 (UTC) Date: Thu, 5 Sep 2024 11:23:14 +0800 From: Baoquan He To: Sourabh Jain Cc: Michael Ellerman , Hari Bathini , kexec@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sachin P Bappalige Subject: Re: [PATCH] kexec/crash: no crash update when kexec in progress Message-ID: References: <20240731152738.194893-1-sourabhjain@linux.ibm.com> <87v80lnf8d.fsf@mail.lhotse> <10c666ae-d528-4f49-82e9-8e0fee7099e0@linux.ibm.com> <355b58b1-6c51-4c42-b6ea-dcd6b1617a18@linux.ibm.com> <1e4a8e18-cda9-45f5-a842-8ffcd725efc9@linux.ibm.com> <0dd94920-b13f-4da7-9ea6-4f008af1f4b3@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0dd94920-b13f-4da7-9ea6-4f008af1f4b3@linux.ibm.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 On 09/04/24 at 02:55pm, Sourabh Jain wrote: > Hello Baoquan, > > On 30/08/24 16:47, Baoquan He wrote: > > On 08/20/24 at 12:10pm, Sourabh Jain wrote: > > > Hello Baoquan, > > > ......snip... > > > 2. A patch to return early from the `crash_handle_hotplug_event()` function > > > if `kexec_in_progress` is > > >    set to True. This is essentially my original patch. > > There's a race gap between the kexec_in_progress checking and the > > setting it to true which Michael has mentioned. > > The window where kernel is holding kexec_lock to do kexec boot > but kexec_in_progress is yet not set to True. > > If kernel needs to handle crash hotplug event, the function > crash_handle_hotplug_event()  will not get the kexec_lock and > error out by printing error message about not able to update > kdump image. But you wanted to avoid the erroring out if it's being in kernel_kexec(). Now you are seeing at least one the noising message, aren't you? > > I think it should be fine. Given that lock is already taken for > kexec kernel boot. > > Am I missing something major? > > > That's why I think > > maybe checking kexec_in_progress after failing to retriving > > __kexec_lock is a little better, not very sure. > > Try for kexec lock before kexec_in_progress check will not solve > the original problem this patch trying to solve. > > You proposed the below changes earlier: > > - if (!kexec_trylock()) { > + if (!kexec_trylock() && kexec_in_progress) { > pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n"); > crash_hotplug_unlock(); Ah, I meant as below, but wrote it mistakenly. diff --git a/kernel/crash_core.c b/kernel/crash_core.c index 63cf89393c6e..e7c7aa761f46 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -504,7 +504,7 @@ int crash_check_hotplug_support(void) crash_hotplug_lock(); /* Obtain lock while reading crash information */ - if (!kexec_trylock()) { + if (!kexec_trylock() && !kexec_in_progress) { pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n"); crash_hotplug_unlock(); return 0; > > > Once the kexec_in_progress is set to True there is no way one can get > kexec_lock. So kexec_trylock() before kexec_in_progress is not helpful > for the problem I am trying to solve. With your patch, you could still get the error message if the race gap exist. With above change, you won't get it. Please correct me if I am wrong.