Messages in this thread Patch in this message | | | Date | Wed, 16 May 2012 18:09:36 -0700 | From | Frank Rowand <> | Subject | [PATCH RT 2/2] fix printk flush of messages |
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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
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