On Fri 2021-04-02 11:14:18, Sergey Senozhatsky wrote: > On (21/04/01 16:17), Petr Mladek wrote: > > > For the long term, we should introduce a printk-context API that allows > > > callers to perfectly pack their multi-line output into a single > > > entry. We discussed [0][1] this back in August 2020. > > > > We need a "short" term solution. There are currently 3 solutions: > > > > 1. Keep nmi_safe() and all the hacks around. > > > > 2. Serialize nmi_cpu_backtrace() by a spin lock and later by > > the special lock used also by atomic consoles. > > > > 3. Tell complaining people how to sort the messed logs. > > Are we talking about nmi_cpu_backtrace()->dump_stack() or some > other path? It is about serializing if (regs) show_regs(regs); else dump_stack(); in nmi_cpu_backtrace() when it is triggered on many(all) CPUs at the same time. > dump_stack() seems to be already serialized by `dump_lock`. Hmm, > show_regs() is not serialized, seems like it should be under the > same `dump_lock` as dump_stack(). Ah, I think that you already mentioned it in the past and I forget it. Yes, we would need to synchronize all these dump/show functions using the same lock. It is already the lock that might be taken recursively on the same CPU. In each case, we must not introduce another lock in nmi_cpu_backtrace() because it might cause deadlock with @dump_lock. Anyway, I would really like to keep the dumps serialized. So, we either need to use the same lock everywhere or we need to keep nmi_safe buffers for now. I would like to remove the nmi_safe buffers in the long term but I am fine with doing it later after the consoles rework. I'll leave the prioritization for John who is doing the work and might have some preferences. Best Regards, Petr _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
