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 8DB07C43219 for ; Tue, 17 May 2022 10:58:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344761AbiEQK6X (ORCPT ); Tue, 17 May 2022 06:58:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344691AbiEQK6U (ORCPT ); Tue, 17 May 2022 06:58:20 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 13820483AA; Tue, 17 May 2022 03:58:18 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 97F9F21CB7; Tue, 17 May 2022 10:58:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1652785097; h=from:from:reply-to: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=UpU3PwW0+vEopHT6mwlEtKZnt5vjcj6K5z6p2RvwFDI=; b=A62HHwy96rt3Peh/2oQoJb/W5OQ8Z85j1RGtcSopCMAn7XlytDk/24zuEW9Tpga7/Yq/ue yQKQnkJYG61eGpGqLTfCCGX/srVGllxHF23XScgduJU8Byym34HyS4Bk1MWh3Z8Rwo0Y9Q s5hDkQjh35sYKTX8Zcjp7xwrzg3RpvU= Received: from suse.cz (unknown [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 5CD572C141; Tue, 17 May 2022 10:58:15 +0000 (UTC) Date: Tue, 17 May 2022 12:58:15 +0200 From: Petr Mladek To: "Guilherme G. Piccoli" 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 Subject: Re: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path Message-ID: References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-6-gpiccoli@igalia.com> <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> Precedence: bulk List-ID: X-Mailing-List: linux-remoteproc@vger.kernel.org On Tue 2022-05-10 10:00:58, Guilherme G. Piccoli wrote: > 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. No problem. It is not worth the effort. > 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. Yup. Best Regards, Petr 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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 37B22C433F5 for ; Tue, 17 May 2022 23:23:52 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4L2sd243Lxz3cBw for ; Wed, 18 May 2022 09:23:50 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=suse.com header.i=@suse.com header.a=rsa-sha256 header.s=susede1 header.b=A62HHwy9; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=suse.com (client-ip=195.135.220.28; helo=smtp-out1.suse.de; envelope-from=pmladek@suse.com; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=suse.com header.i=@suse.com header.a=rsa-sha256 header.s=susede1 header.b=A62HHwy9; dkim-atps=neutral Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) (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 lists.ozlabs.org (Postfix) with ESMTPS id 4L2Y4t225Qz3bq3 for ; Tue, 17 May 2022 20:58:21 +1000 (AEST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 97ABB21CB1; Tue, 17 May 2022 10:58:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1652785097; h=from:from:reply-to: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=UpU3PwW0+vEopHT6mwlEtKZnt5vjcj6K5z6p2RvwFDI=; b=A62HHwy96rt3Peh/2oQoJb/W5OQ8Z85j1RGtcSopCMAn7XlytDk/24zuEW9Tpga7/Yq/ue yQKQnkJYG61eGpGqLTfCCGX/srVGllxHF23XScgduJU8Byym34HyS4Bk1MWh3Z8Rwo0Y9Q s5hDkQjh35sYKTX8Zcjp7xwrzg3RpvU= Received: from suse.cz (unknown [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 5CD572C141; Tue, 17 May 2022 10:58:15 +0000 (UTC) Date: Tue, 17 May 2022 12:58:15 +0200 From: Petr Mladek To: "Guilherme G. Piccoli" Subject: Re: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path Message-ID: References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-6-gpiccoli@igalia.com> <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> X-Mailman-Approved-At: Wed, 18 May 2022 09:23:23 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-hyperv@vger.kernel.org, halves@canonical.com, gregkh@linuxfoundation.org, peterz@infradead.org, alejandro.j.jimenez@oracle.com, linux-remoteproc@vger.kernel.org, feng.tang@intel.com, linux-mips@vger.kernel.org, hidehiro.kawai.ez@hitachi.com, sparclinux@vger.kernel.org, will@kernel.org, tglx@linutronix.de, linux-leds@vger.kernel.org, linux-s390@vger.kernel.org, mikelley@microsoft.com, john.ogness@linutronix.de, bhe@redhat.com, corbet@lwn.net, paulmck@kernel.org, fabiomirmar@gmail.com, x86@kernel.org, zhenwei pi , mingo@redhat.com, bcm-kernel-feedback-list@broadcom.com, xen-devel@lists.xenproject.org, dyoung@redhat.com, vgoyal@redhat.com, linux-xtensa@linux-xtensa.org, dave.hansen@linux.intel.com, keescook@chromium.org, arnd@arndb.de, linux-pm@vger.kernel.org, Mihai Carabas , coresight@lists.linaro.org, Shile Zhang , linux-um@lists.infradead.org, rostedt@goodmis.org, rcu@vger.kernel.org, Wang ShaoBo , bp@alien8.de, luto@kernel.org, linux-tegra@vger.kernel.org, openipmi-developer@lists.sourceforge.net, andriy.shevchenko@linux.intel.com, vkuznets@redhat.com, linux-arm-kernel@lists.infradead.org, linux-edac@vger.kernel.org, jgross@suse.com, linux-parisc@vger.kernel.org, netdev@vger.kernel.org, kernel@gpiccoli.net, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, stern@rowland.harvard.edu, senozhatsky@chromium.org, d.hatayama@jp.fujitsu.com, mhiramat@kernel.org, kernel-dev@igalia.com, linux-alpha@vger.kernel.org, Christophe JAILLET , akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue 2022-05-10 10:00:58, Guilherme G. Piccoli wrote: > 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. No problem. It is not worth the effort. > 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. Yup. Best Regards, Petr From mboxrd@z Thu Jan 1 00:00:00 1970 From: Petr Mladek Date: Tue, 17 May 2022 12:58:15 +0200 Subject: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path In-Reply-To: <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-6-gpiccoli@igalia.com> <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kexec@lists.infradead.org On Tue 2022-05-10 10:00:58, Guilherme G. Piccoli wrote: > 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. No problem. It is not worth the effort. > 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. Yup. Best Regards, Petr From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 17 May 2022 12:58:15 +0200 From: Petr Mladek Subject: Re: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path Message-ID: References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-6-gpiccoli@igalia.com> <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: "Guilherme G. Piccoli" 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 On Tue 2022-05-10 10:00:58, Guilherme G. Piccoli wrote: > 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. No problem. It is not worth the effort. > 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. Yup. Best Regards, Petr _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um From mboxrd@z Thu Jan 1 00:00:00 1970 From: Petr Mladek Subject: Re: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path Date: Tue, 17 May 2022 12:58:15 +0200 Message-ID: References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-6-gpiccoli@igalia.com> <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1652785097; h=from:from:reply-to: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=UpU3PwW0+vEopHT6mwlEtKZnt5vjcj6K5z6p2RvwFDI=; b=A62HHwy96rt3Peh/2oQoJb/W5OQ8Z85j1RGtcSopCMAn7XlytDk/24zuEW9Tpga7/Yq/ue yQKQnkJYG61eGpGqLTfCCGX/srVGllxHF23XScgduJU8Byym34HyS4Bk1MWh3Z8Rwo0Y9Q s5hDkQjh35sYKTX8Zcjp7xwrzg3RpvU= Content-Disposition: inline In-Reply-To: <0a20dd06-f459-638e-cb4d-8255ab1a1f23@igalia.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Guilherme G. Piccoli" 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 On Tue 2022-05-10 10:00:58, Guilherme G. Piccoli wrote: > 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. No problem. It is not worth the effort. > 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. Yup. Best Regards, Petr