Messages in this thread | | | Date | Mon, 21 May 2012 13:10:56 -0700 | From | Venkat Subbiah <> | Subject | Re: [PATCH RT 2/2] fix printk flush of messages |
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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@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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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