printk: use rcuidle console tracepoint

Linux Kernel / Linux Kernel - Sergey Senozhatsky [gmail.com] - 18 February 2017 20:27 EST

Use rcuidle console tracepoint because, apparently, it may be issued from an idle CPU:

hw-breakpoint: Failed to enable monitor mode on CPU 0. hw-breakpoint: CPU 0 failed to disable vector catch


[ ERR: suspicious RCU usage. ] 4.10.0-rc8-next-20170215+ #119 Not tainted

./include/trace/events/printk.h:32 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

RCU used illegally from idle CPU! rcu_scheduler_active = 2, debug_locks = 0 RCU used illegally from extended quiescent state! 2 locks held by swapper/0/0: #0: (cpu_pm_notifier_lock){......}, at: [] cpu_pm_exit+0x10/0x54 #1: (console_lock){+.+.+.}, at: [] vprintk_emit+0x264/0x474

stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc8-next-20170215+ #119 Hardware name: Generic OMAP4 (Flattened Device Tree) console_unlock
vprintk_emit
vprintk_default printk reset_ctrl_regs dbg_cpu_pm_notify notifier_call_chain cpu_pm_exit omap_enter_idle_coupled cpuidle_enter_state cpuidle_enter_state_coupled do_idle cpu_startup_entry start_kernel

This RCU warning, however, is suppressed by lockdep_off() in printk(). lockdep_off() increments the ->lockdep_recursion counter and thus disables RCU_LOCKDEP_WARN() and debug_lockdep_rcu_enabled(), which want lockdep to be enabled "current->lockdep_recursion == 0".

Link: http://lkml.kernel.org/r/20170217015932.11898-1-sergey.senozhatsky@gmail.com

fc98c3c printk: use rcuidle console tracepoint
kernel/printk/printk.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Upstream: git.kernel.org


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