On 2015年08月12日 10:04, Greg Kroah-Hartman wrote: > On Wed, Aug 12, 2015 at 09:53:58AM +0800, Pan Xinhui wrote: >> Hi, Greg >> thanks for your reply! >> On 2015年08月12日 02:16, Greg Kroah-Hartman wrote: >>> On Tue, Aug 11, 2015 at 07:23:01PM +0800, Pan Xinhui wrote: >>>> From: Pan Xinhui <xinhuix....@intel.com> >>>> >>>> printk can be called in any context, It's very useful to output debug >>>> info. >>>> >>>> But it might cause very bad issues on some special cases. For example, >>>> some driver hit errors, and it dumps many messages like reg values, etc. >>>> >>>> Sometimes, printk is called when irqs disabled. This is OKay if there is >>>> a few messages. But What would happen if many messages outputted by other >>>> drivers at same time. >>>> >>>> Here is the scenario. >>>> CPUA CPUB >>>> local_irq_save(flags); >>>> printk() >>>> while(..) { --> console_unlock >>>> printk(...); >>>> //hundreds or thousands loops >>>> } //all messages flushed out to consoles >>>> local_irq_restore(flags); >>>> >>> >>> Where are you seeing this type of scenario "in the wild"? Or is this >>> just a "debug/bringup hardware" issue? We shouldn't be ever stuck in a >>> printk that prints hundreds or thousands of loops, if so, we need to fix >>> the kernel code that does that, as we do have control over this. >>> >> >> Sorry for misleading. these loops are just an example. In real world, >> there are many pr_info/pr_err when some drivers hit device errors to >> dump debug information. > > That's not good, they should use dev_dbg() for that instead. > Agree, We changed some codes to use dev_dbg(). But some errors still need be outputted immediately. But when we enabled dynamic debug. there is not much difference... printk issue still hit.
>> There is camera and sound test(multimedia test) in our side, we enable >> dynamic_debug to collect logs to fix some weird issues. sound driver >> will dump many reg/memory values, and camera will output a few logs >> with irqs disabled. So we hit this printk issues very frequently, and >> it blocks our tests indeed. > > Maybe those memory value dumps should be done through debugfs instead of > printk? > These reg/memory runtime values must be outputted in time, they have changed at any time.. >> As printk is announced that it could be used in most context, So I >> prefer to enhance the stability of printk to handle such case. > > Stability is nice, but using printk for things it was never ment to be > used for, isn't good. Especially if you are forced to add additional > complexity to the printk logic just for these corner cases that no one > uses :) > printk is very good, it does work in very complex context, including in interrupt, etc. However if we could make it better, then why not :) My patch is a little complex. Sorry for that. I would try to work out V2. thanks xinhui > thanks, > > greg k-h > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/