On 05/16/2012 06:09 PM, Frank Rowand wrote:
Updates console-make-rt-friendly.patch
#ifdef CONFIG_PREEMPT_RT_FULL, printk() output is never flushed by
printk() because:
So this is an issue for printk() itself and is not just for early_printk()?
# 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()
As I read it console_trylock_for_printk() is called from printk() but in
code it is called from vprintk()
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@xxxxxxxxxxx>
---
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
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