Messages in this thread | | | Date | Mon, 14 Feb 2022 16:35:18 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online() |
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On (22/02/11 17:05), Petr Mladek wrote: > On Mon 2022-02-07 20:49:13, John Ogness wrote: [..] > The problem is the commit ac25575203c11145066ea ("[PATCH] CPU hotplug > printk fix"). It suggests that per-CPU data of slab are freed during > hotplug. > > There are many other things that are manipulated during cpu hotplug. > And there are the two notifiers "printk:dead" and "printk:online", > see printk_late_init(). Maybe, we should use them to decide whether > the non-trivial consoles are callable during CPU hotplug.
Great findings. Looks like we only set __printk_percpu_data_ready to true and never set it back to false, relying on cpu_online() in such cases. But here's the thing: we have printk_percpu_data_ready() in __printk_recursion_counter() and in wake_up_klogd() and in defer_console_output(), but why we never check __printk_percpu_data_ready in __down_trylock_console_sem()/__up_console_sem() and more importantly in console_trylock_spinning() and those do access this_cpu() in printk safe enter/exit. Am I missing something?
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