Currently, if printk lock (logbuf_lock) is held by other thread during crash, there is a chance of deadlocking the crash on next printk, and blocking a possibly desired kdump.
At the start of default_machine_crash_shutdown, make printk enter NMI context, as it will use per-cpu buffers to store the message, and avoid locking logbuf_lock. Suggested-by: Michael Ellerman <m...@ellerman.id.au> Signed-off-by: Leonardo Bras <leobra...@gmail.com> --- Changes since v2: - Changes usage of printk_nmi_enter() to nmi_enter() (Suggested by Nick Piggin) Changes since v1: - Added in-code comment explaining the need of context change - Function moved to the start of default_machine_crash_shutdown, to avoid locking any printk on crashing routine. - Title was 'Use NMI context for printk after crashing other CPUs' --- arch/powerpc/kexec/crash.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c index d488311efab1..53c5cf9b6d3c 100644 --- a/arch/powerpc/kexec/crash.c +++ b/arch/powerpc/kexec/crash.c @@ -16,6 +16,7 @@ #include <linux/delay.h> #include <linux/irq.h> #include <linux/types.h> +#include <linux/hardirq.h> #include <asm/processor.h> #include <asm/machdep.h> @@ -311,6 +312,13 @@ void default_machine_crash_shutdown(struct pt_regs *regs) unsigned int i; int (*old_handler)(struct pt_regs *regs); + /* + * Avoid hardlocking with irresponsive CPU holding logbuf_lock, + * by using printk nmi_context + */ + if (!in_nmi()) + nmi_enter(); + /* * This function is only called after the system * has panicked or is otherwise in a critical state. -- 2.25.4