From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: [PATCH RT 1/2] fix printk flush of messages Date: Fri, 24 Aug 2012 23:12:20 -0400 Message-ID: <20120825031657.843877293@goodmis.org> References: <20120825031219.772181128@goodmis.org> Cc: Thomas Gleixner , Carsten Emde , John Kacur , Frank Rowand , Frank To: linux-kernel@vger.kernel.org, linux-rt-users Return-path: Content-Disposition: inline; filename=0001-fix-printk-flush-of-messages.patch Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org 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 Cc: Frank Link: http://lkml.kernel.org/r/4FB44FD0.4090800@am.sony.com Signed-off-by: Thomas Gleixner --- 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