From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shuge Subject: Re: [BUG]: when printk too more through serial, cpu up is failed. Date: Fri, 15 Mar 2013 09:26:26 +0800 Message-ID: <514278C2.3020900@gmail.com> References: <5141D5E6.4060001@gmail.com> <20130314140553.GA4895@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-pb0-f47.google.com ([209.85.160.47]:41701 "EHLO mail-pb0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751970Ab3COBeO (ORCPT ); Thu, 14 Mar 2013 21:34:14 -0400 In-Reply-To: <20130314140553.GA4895@kroah.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Greg KH Cc: linux-kernel@vger.kernel.org, Kevin , linux-serial@vger.kernel.org, Russell King , Tejun Heo =E4=BA=8E 2013=E5=B9=B403=E6=9C=8814=E6=97=A5 22:05, Greg KH =E5=86=99=E9= =81=93: > On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote: >> Hi all, >> When the kernel printk too many log, the cpu is failed to come = online. >> The problem is this: >> For example, cpu0 bring up cpu1: >> >> a. cpu0 call cpu_up: >> cpu_up() >> ->_cpu_up() >> ->__cpu_notify(CPU_UP_PREPARE) >> ->__cpu_up() >> ->boot_secondary() >> # ->wait_for_completion_timeout(&cpu_running, msecs_to_jiffire= s(1000)) >> -> if (!cpu_online(cpu)) { >> pr_crit("CPU%u: failed to come online\n", cpu); >> ret =3D -EIO; >> } >> ->cpu_notify(CPU_ONLINE) >> >> b. cpu1 enter kernel: >> secondary_start_kernel() >> @ ->printk("CPU%u: Booted secondary processor\n", cpu) >> * ->calibrate_delay() >> ->set_cpu_online() >> ->complete(cpu_running) >> ->cpumask_set_cpu() >> >> While cpu0 run to mark #, which wait that cpu1 complete >> cpu_running, and set online. >> Generally, cpu0 can get it. But if the __log_buf is too large or >> other threads write >> it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is >> busy outputing >> buffer, which cost time more than 1s, and cpu1 have not join in >> sched, so cpu0 wait it timeout. >> By reading printk.c, I found that can_use_console() always retur= n >> true, which be called by >> console_trylock_for_printk(). Because, have_callable_console() >> return ture always, if the console >> driver set CON_ANYTIME flag. I think that cpu should not output the >> __log_buf in coming online, >> even though have_callable_console() is true. >> >> /* >> * Can we actually use the console at this time on this cpu? >> * >> * Console drivers may assume that per-cpu resources have >> * been allocated. So unless they're explicitly marked as >> * being able to cope (CON_ANYTIME) don't call them until >> * this CPU is officially up. >> */ >> static inline int can_use_console(unsigned int cpu) >> { >> return cpu_online(cpu) || have_callable_console(); >> } >> >> In can_use_console, why not is &&, but ||? >> >> Kernel Version: 3.3.0 > Why such an old and obsolete kernel version? Please try this on 3.8, > lots of work have gone into the printk area that should have solved t= his > issue. > > greg k-h I saw the printk.c in version 3.9, it still check=20 console_trylock_for_printk() to decide to call console_unlock. In=20 vprintk_emit(), cpu1 also have the opportunity to execute=20 console_unlock() at coming online time. Once cpu which is coming online can output buffer, nothing can interrup= t=20 it until buffer is empty.But we can't ensure that none always write the= =20 __log_buf. It is danger! I think, the solution is that we should preven= t=20 to use console at coming online. -- To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html