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