Re: [PATCH] printk: use rcuidle console tracepoint

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Fri, Feb 17, 2017 at 10:59:32AM +0900, Sergey Senozhatsky wrote:
> Use rcuidle console tracepoint because, apparently, it may be issued
> from an idle CPU:
> 
> [    2.581939] hw-breakpoint: Failed to enable monitor mode on CPU 0.
> [    2.591613] hw-breakpoint: CPU 0 failed to disable vector catch
> [    2.597686]
> [    2.597717] ===============================
> [    2.597717] [ ERR: suspicious RCU usage.  ]
> [    2.597717] 4.10.0-rc8-next-20170215+ #119 Not tainted
> [    2.597717] -------------------------------
> [    2.597717] ./include/trace/events/printk.h:32 suspicious rcu_dereference_check() usage!
> [    2.597717]
> [    2.597717] other info that might help us debug this:
> [    2.597717]
> [    2.597717]
> [    2.597717] RCU used illegally from idle CPU!
> [    2.597717] rcu_scheduler_active = 2, debug_locks = 0
> [    2.597747] RCU used illegally from extended quiescent state!
> [    2.597747] 2 locks held by swapper/0/0:
> [    2.597747]  #0:  (cpu_pm_notifier_lock){......}, at: [<c0237e2c>] cpu_pm_exit+0x10/0x54
> [    2.597747]  #1:  (console_lock){+.+.+.}, at: [<c01ab350>] vprintk_emit+0x264/0x474
> [    2.597747]
> [    2.597747] stack backtrace:
> [    2.597778] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc8-next-20170215+ #119
> [    2.597778] Hardware name: Generic OMAP4 (Flattened Device Tree)
> [    2.597778] [<c0110228>] (unwind_backtrace) from [<c010c224>] (show_stack+0x10/0x14)
> [    2.597778] [<c010c224>] (show_stack) from [<c04ca8a0>] (dump_stack+0xac/0xe0)
> [    2.597778] [<c04ca8a0>] (dump_stack) from [<c01ab084>] (console_unlock+0x5e8/0x650)
> [    2.597778] [<c01ab084>] (console_unlock) from [<c01ab35c>] (vprintk_emit+0x270/0x474)
> [    2.597778] [<c01ab35c>] (vprintk_emit) from [<c01ab6f0>] (vprintk_default+0x20/0x28)
> [    2.597808] [<c01ab6f0>] (vprintk_default) from [<c0250c94>] (printk+0x20/0x30)
> [    2.597808] [<c0250c94>] (printk) from [<c0111004>] (reset_ctrl_regs+0x108/0x288)
> [    2.597808] [<c0111004>] (reset_ctrl_regs) from [<c0111220>] (dbg_cpu_pm_notify+0x28/0x30)
> [    2.597808] [<c0111220>] (dbg_cpu_pm_notify) from [<c015f3ac>] (notifier_call_chain+0x44/0x80)
> [    2.597808] [<c015f3ac>] (notifier_call_chain) from [<c0237e48>] (cpu_pm_exit+0x2c/0x54)
> [    2.597808] [<c0237e48>] (cpu_pm_exit) from [<c0126ca0>] (omap_enter_idle_coupled+0x80/0x208)
> [    2.597808] [<c0126ca0>] (omap_enter_idle_coupled) from [<c0680d80>] (cpuidle_enter_state+0x118/0x4ac)
> [    2.597808] [<c0680d80>] (cpuidle_enter_state) from [<c0682e54>] (cpuidle_enter_state_coupled+0x3a8/0x40c)
> [    2.597839] [<c0682e54>] (cpuidle_enter_state_coupled) from [<c0190c04>] (do_idle+0x1a4/0x218)
> [    2.597839] [<c0190c04>] (do_idle) from [<c0190ffc>] (cpu_startup_entry+0x18/0x1c)
> [    2.597839] [<c0190ffc>] (cpu_startup_entry) from [<c0c00c40>] (start_kernel+0x35c/0x3d4)
> [    2.597839] [<c0c00c40>] (start_kernel) from [<8000807c>] (0x8000807c)
> 
> 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".
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Reported-by: Tony Lindgren <tony@atomide.com>
> Tested-by: Tony Lindgren <tony@atomide.com>
> Cc: <stable@vger.kernel.org> [3.4+]

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
>  kernel/printk/printk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 7180088cbb23..34da86e73d00 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1563,7 +1563,7 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
>  {
>  	struct console *con;
> 
> -	trace_console(text, len);
> +	trace_console_rcuidle(text, len);
> 
>  	if (!console_drivers)
>  		return;
> -- 
> 2.11.1
>