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 80E53C433EF for ; Tue, 10 May 2022 13:02:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242204AbiEJNGk (ORCPT ); Tue, 10 May 2022 09:06:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51394 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242191AbiEJNF7 (ORCPT ); Tue, 10 May 2022 09:05:59 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9EE02618FC; Tue, 10 May 2022 06:02:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=JWyep5EFfEPXN0/UUFSWkvsTwBT4W/fOxchQHhKa4RM=; b=sx6DF8PoUIO1mHu5cZY1RxwoA9 niB1KysO8rrmF0zp8Z8GTN/NtCj2d4QR4yv3E2E5W17RExRi8A0KAmcw+03c1G1ooU/Pm21U+zIEh 0zp/hEbV2HUhNtVPnHFdp5DB6IlN6W8R3VOm7oythqBX2GRaLpOj+rJPIjIYg4FRTMuO76QGoLFC6 YTJOWt6WzTDBhnK8IJgaIHAnWrK2atb9lCglavMKbFL3MElzKi625NHcWNdIldxGBU96c/pM4S0g8 wJXsSSNXtcQC2Akbyu07xQvQmC9j0tVwKiovTIAilxmwfqg23OLqdBOLywiRmkuVFih5uNhaytVXp cz9YcgaQ==; Received: from [177.183.162.244] (helo=[192.168.0.5]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1noPUd-0004lT-6O; Tue, 10 May 2022 15:01:35 +0200 Message-ID: <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> Date: Tue, 10 May 2022 10:00:58 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path Content-Language: en-US To: Petr Mladek Cc: akpm@linux-foundation.org, bhe@redhat.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, coresight@lists.linaro.org, linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-leds@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-pm@vger.kernel.org, linux-remoteproc@vger.kernel.org, linux-s390@vger.kernel.org, linux-tegra@vger.kernel.org, linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org, netdev@vger.kernel.org, openipmi-developer@lists.sourceforge.net, rcu@vger.kernel.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bp@alien8.de, corbet@lwn.net, d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com, dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org, mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com, jgross@suse.com, john.ogness@linutronix.de, keescook@chromium.org, luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, stern@rowland.harvard.edu, tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com, will@kernel.org, Christophe JAILLET , Mihai Carabas , Shile Zhang , Wang ShaoBo , zhenwei pi References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-6-gpiccoli@igalia.com> From: "Guilherme G. Piccoli" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/05/2022 09:14, Petr Mladek wrote: > [...] >> With that said, it's dangerous to use regular spinlocks in such path, >> as introduced by commit b3c0f8774668 ("misc/pvpanic: probe multiple instances"). >> This patch fixes that by replacing regular spinlocks with the trylock >> safer approach. > > It seems that the lock is used just to manipulating a list. A super > safe solution would be to use the rcu API: rcu_add_rcu() and > list_del_rcu() under rcu_read_lock(). The spin lock will not be > needed and the list will always be valid. > > The advantage would be that it will always call members that > were successfully added earlier. That said, I am not familiar > with pvpanic and am not sure if it is worth it. > >> It also fixes an old comment (about a long gone framebuffer code) and >> the notifier priority - we should execute hypervisor notifiers early, >> deferring this way the panic action to the hypervisor, as expected by >> the users that are setting up pvpanic. > > This should be done in a separate patch. It changes the behavior. > Also there might be a discussion whether it really should be > the maximal priority. > > Best Regards, > Petr Thanks for the review Petr. Patch was already merged - my goal was to be concise, i.e., a patch per driver / module, so the patch kinda fixes whatever I think is wrong with the driver with regards panic handling. Do you think it worth to remove this patch from Greg's branch just to split it in 2? Personally I think it's not worth, but opinions are welcome. About the RCU part, this one really could be a new patch, a good improvement patch - it makes sense to me, we can think about that after the fixes I guess. Cheers, Guilherme