Messages in this thread | | | Date | Fri, 30 Jun 2017 23:28:51 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [RFC][PATCHv3 2/5] printk: introduce printing kernel thread |
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On (06/30/17 09:33), Steven Rostedt wrote: [..] > > "something sometime in the future" is equal to "no one". > > > > we must stay and continue printing. because it gives the right > > answer - "current process and right now. until someone else > > (+printk_kthread) takes over". > > Would it be acceptable to have a user knob that allows for it not to > happen? That is, let the user of the kernel decide if they care about > critical prints or not? If a knob says, "only print X, then offload" > would that be allowed. Of course the default would be "only print ALL > OF IT" to keep the current behavior.
I'm sorry, I'm not sure I got your question right (I need some rest probably).
I guess the question was, a knob that would determine what happens after current wakes up printk_kthread -- does it stay in console_unlock() and wait for new console_sem owner, printing the messages in the meantime, or goes all in and expects printk_kthread or anything else to lock console_sem at some point and flush the remaining messages. is that correct? we can do this (well, I'm absolutely not in position to say "we can't do this" :) ). I guess the sort of a problem we have now is that we can't guarantee that wake_up() will actually wake_up printk_kthread. but if user requests it, then well... it might be easier to adjust watchdog timeout value ;) just kidding. or may be I misunderstood your question.
or... another silly idea... shall we start touching the lockup watchdog per-cpu counters on the CPU that has:
a) woken up printk_kthread b) but is still in console_unlock() waiting for the new console_sem owner?
...
or we, may be, can add a new sysrq that would flush logbuf messages... the same way as console_flush_on_panic() does. just in case if wake_up didn't work.... or is there already a sysrq for that?
-ss
> A lot of times the console isn't recorded to debug hard lock ups. I > know most desktops running a GUI do not. When ever my workstation locks > up, and it has no serial, I don't get to see the dmesg at all. In this > situation, I don't care if the prints are offloaded or not. > > -- Steve >
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