Messages in this thread | | | Date | Thu, 1 Sep 2016 10:17:33 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH] printk/nmi: avoid direct printk()-s from __printk_nmi_flush() |
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On Thu 2016-09-01 16:55:07, Sergey Senozhatsky wrote: > On (08/30/16 13:19), Petr Mladek wrote: > > > > I see. But then we will need to be more careful because printk_func > > and printk_func_saved will be manipulated in different contexts: > > normal, irq, nmi. A solution might be using an atomic counter > > and selecting the right vprintk_func according to the value. > > alt_printk_enter() must be done with local IRQs disabled. so IRQ cannot > race with `normal' alt_printk. other IRQs cannot race with the current IRQ, > because we have local IRQs disabled. the only thing that can race here is - NMI. > both `normal' and IRQ alt_printk can use the same per-CPU buffer, they never > race. NMI needs to have its own.
Yes. Well, my concern was how to atomically change the printk_func pointer and save the previous value at the same time. You could not use locks because NMIs are involved.
Best Regards, Petr
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