[PATCH RT 1/2] fix printk flush of messages

[Steven Rostedt <rostedt@goodmis.org>]

[-- Attachment #1: 0001-fix-printk-flush-of-messages.patch --]
[-- Type: text/plain, Size: 1778 bytes --]

Updates console-make-rt-friendly.patch

#ifdef CONFIG_PREEMPT_RT_FULL, printk() output is never flushed by
printk() because:

   # some liberties taken in this pseudo-code to make it easier to follow
   printk()
      vprintk()
         raw_spin_lock(&logbuf_lock)
            # increment preempt_count():
            preempt_disable()
      result = console_trylock_for_printk()
         retval = 0
         # lock will always be false, because preempt_count() will be >= 1
         lock = ... && !preempt_count()
         if (lock)
            retval = 1
         return retval
      # result will always be false since lock will always be false
      if (result)
         console_unlock()
            # this is where the printk() output would be flushed

On system boot some printk() output is flushed because register_console()
and tty_open() call console_unlock().

This change also fixes the problem that was previously fixed by
preempt-rt-allow-immediate-magic-sysrq-output-for-preempt_rt_full.patch

Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Frank <Frank_Rowand@sonyusa.com>
Link: http://lkml.kernel.org/r/4FB44FD0.4090800@am.sony.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/printk.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 9eabbbb..66e83e5 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -836,7 +836,7 @@ static int console_trylock_for_printk(unsigned int cpu, unsigned long flags)
 	int retval = 0, wake = 0;
 #ifdef CONFIG_PREEMPT_RT_FULL
 	int lock = (!early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
-		!preempt_count()) || sysrq_in_progress;
+		(preempt_count() <= 1)) || sysrq_in_progress;
 #else
 	int lock = 1;
 #endif
-- 
1.7.10.4