lkml.org 
[lkml]   [2012]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH RT 2/2] fix printk flush of messages

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>

---
kernel/printk.c | 2 1 + 1 - 0 !
1 file changed, 1 insertion(+), 1 deletion(-)

Index: b/kernel/printk.c
===================================================================
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -847,7 +847,7 @@ static int console_trylock_for_printk(un
int retval = 0, wake = 0;
#ifdef CONFIG_PREEMPT_RT_FULL
int lock = !early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
- !preempt_count();
+ (preempt_count() <= 1);
#else
int lock = 1;
#endif


\
 
 \ /
  Last update: 2012-05-17 03:41    [W:0.091 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site