This is a note to let you know that I've just added the patch titled printk: use rcuidle console tracepoint to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: printk-use-rcuidle-console-tracepoint.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From fc98c3c8c9dcafd67adcce69e6ce3191d5306c9c Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> Date: Sat, 18 Feb 2017 03:42:54 -0800 Subject: printk: use rcuidle console tracepoint From: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> commit fc98c3c8c9dcafd67adcce69e6ce3191d5306c9c upstream. 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: [<c0237e2c>] cpu_pm_exit+0x10/0x54 #1: (console_lock){+.+.+.}, at: [<c01ab350>] 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@xxxxxxxxx Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Reported-by: Tony Lindgren <tony@xxxxxxxxxxx> Tested-by: Tony Lindgren <tony@xxxxxxxxxxx> Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Cc: Petr Mladek <pmladek@xxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Tony Lindgren <tony@xxxxxxxxxxx> Cc: Russell King <rmk@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/printk/printk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1436,7 +1436,7 @@ static void call_console_drivers(int lev { struct console *con; - trace_console(text, len); + trace_console_rcuidle(text, len); if (level >= console_loglevel && !ignore_loglevel) return; Patches currently in stable-queue which might be from sergey.senozhatsky.work@xxxxxxxxx are queue-4.4/printk-use-rcuidle-console-tracepoint.patch