Hi all, In kernel before 3.19, when trigger_all_cpu_backtrace() is called on x86, it will trigger an NMI on each CPU and call show_regs(). But this can lead to a hard lock up if the NMI comes in on another printk().
The commit a9edc88093287183ac934be44f295f183b2c62dd (x86/nmi: Perform a safe NMI stack trace on all CPUs) fix this problem on kernel mainline. when the NMI triggers, it switches the printk routine for that CPU to call a NMI safe printk function that records the printk in a per_cpu seq_buf descriptor. After all NMIs have finished recording its data, the seq_bufs are printed in a safe context. But how do we fix this problem in older version of kernel(eg, 3.10 stable)? The 3.10 stable has no "switch printk routine" and "seq_buf" infrastructures. Could anyone give me some ideas? Best Regards Wang Long
