Messages in this thread | | | Date | Fri, 15 Mar 2013 09:26:26 +0800 | From | Shuge <> | Subject | Re: [BUG]: when printk too more through serial, cpu up is failed. |
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于 2013年03月14日 22:05, Greg KH 写道: > 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_jiffires(1000)) >> -> if (!cpu_online(cpu)) { >> pr_crit("CPU%u: failed to come online\n", cpu); >> ret = -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 return >> 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 this > issue. > > greg k-h
I saw the printk.c in version 3.9, it still check console_trylock_for_printk() to decide to call console_unlock. In vprintk_emit(), cpu1 also have the opportunity to execute console_unlock() at coming online time. Once cpu which is coming online can output buffer, nothing can interrupt it until buffer is empty.But we can't ensure that none always write the __log_buf. It is danger! I think, the solution is that we should prevent to use console at coming online. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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