linux-kernel - [PATCH 4.9 16/22] printk: use rcuidle console tracepoint

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Message-Id: <20170221130219.605685993@linuxfoundation.org>
Date:   Tue, 21 Feb 2017 14:03:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Russell King <rmk@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 16/22] printk: use rcuidle console tracepoint

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>

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@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Reported-by: Tony Lindgren <tony@...mide.com>
Tested-by: Tony Lindgren <tony@...mide.com>
Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tony Lindgren <tony@...mide.com>
Cc: Russell King <rmk@...linux.org.uk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/printk/printk.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1564,7 +1564,7 @@ static void call_console_drivers(int lev
 {
 	struct console *con;

-	trace_console(text, len);
+	trace_console_rcuidle(text, len);

 	if (!console_drivers)
 		return;