This is my backport patch series to Fix the problem(backport to 3.10): " 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 solution is described in commit "a9edc88093287183ac934be44f295f183b2c62dd": 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 trace_ seqs are printed in a safe context. The solution use "switch printk routine" and "seq_buf" infrastructures, but the 3.10 stable have no both of them. The patch 1-13 backport the "seq_buf" infrastructures. in detail, patch 1, 2 and 6 only backport "seq_buf" related code. The patch 14-15 backport the "switch printk routine". The patch 16-17 is the patch to print all cpu stacks from NMI safely as discussed in https://lkml.org/lkml/2015/5/13/497, in 3.10 stable, this is the only way to solve the problem and the backport code is a bit more. Any thoughts? Sasha Levin (1): x86/nmi: Fix use of unallocated cpumask_var_t Steven Rostedt (Red Hat) (16): tracing: Create seq_buf layer in trace_seq tracing: Convert seq_buf_path() to be like seq_path() tracing: Convert seq_buf fields to be like seq_file fields tracing: Add a seq_buf_clear() helper and clear len and readpos in init seq_buf: Create seq_buf_used() to find out how much was written tracing: Use trace_seq_used() and seq_buf_used() instead of len seq_buf: Add seq_buf_can_fit() helper function tracing: Have seq_buf use full buffer tracing: Add seq_buf_get_buf() and seq_buf_commit() helper functions seq-buf: Make seq_buf_bprintf() conditional on CONFIG_BINARY_PRINTF seq_buf: Move the seq_buf code to lib/ seq_buf: Fix seq_buf_vprintf() truncation seq_buf: Fix seq_buf_bprintf() truncation printk: Add per_cpu printk func to allow printk to be diverted printk/percpu: Define printk_func when printk is not defined x86/nmi: Perform a safe NMI stack trace on all CPUs arch/x86/kernel/apic/hw_nmi.c | 86 +++++++++- include/linux/percpu.h | 4 + include/linux/printk.h | 2 + include/linux/seq_buf.h | 136 ++++++++++++++++ kernel/printk.c | 41 +++-- lib/Makefile | 2 +- lib/seq_buf.c | 359 ++++++++++++++++++++++++++++++++++++++++++ 7 files changed, 617 insertions(+), 13 deletions(-) create mode 100644 include/linux/seq_buf.h create mode 100644 lib/seq_buf.c -- 1.8.3.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html