Messages in this thread | | | Date | Fri, 7 May 2021 18:13:41 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH] printk: stop spining waiter when console resume to flush prb |
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On Thu 2021-05-06 23:07:19, Sergey Senozhatsky wrote: > Thanks for Cc-ing Petr > > On (21/05/06 15:39), Petr Mladek wrote: > > > > Many printk messages might get accumulated when consoles were suspended. > > They are proceed when console_unlock() is called in resume_console(). > > > > The possibility to pass the console lock owner was added to reduce the risk > > of softlockup when too many messages were handled in an atomic context. > > > > Now, resume_console() is always in a preemptible context that is safe > > to handle all accumulated messages. The possibility to pass the console > > lock owner actually makes things worse. The new owner might be in an atomic > > context and might cause softlockup when processing all messages accumulated > > when the console was suspended. > > > > Create new console_unlock_preemptible() that will not allow to pass > > the console lock owner. As a result, all accumulated messages will > > be proceed in the safe preemptible process. > > If we have a lot of pending messages in the logbuf, then there is > something chatty - some context (task, irq) or maybe several contexts. > And those contexts can continue adding messages, while we print them > _exclusively_ from preemptible context only. without ever throttling down > printk() callers - something that console_owner spinning and handover > does for us. And those printk() callers can even preempt > console_unlock_preemptible() and cause delays and lost messages.
Luo, please, correct me if I am wrong.
This patch a about one well defined scenario. The messages are accumulated between suspend_console() and resume_console(). It is "small" part of the system hibernation. And we need to get them out now. There might be many if something special was debugged.
I am pretty sure that Luo did not see any flood of messages:
+ Flood in more contexts would be balanced by switching the console_owner.
+ Flood in one context would be naturally throttled because this context will become the console_owner.
In each case, these messages would be generated after console_resume(). Luo's original patch was explicitly talking about messages accumulated during the suspend.
Luo, could you please provide some log showing the problem?
Best Regards, Petr
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