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Subject[RT] Race condition on bug output.
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Date
Hi Ingo,

I found a race condition in my kernel which can also be found in yours.
When I trigger the printk in check_periodic_interval, interrupts are
turned on in release_console_sem. Unfortunately, this can have an
interrupt go off there (since they are turned back on there) and the
write_lock system_time_lock will be taken again, thus producing a
deadlock.

I'm not sure if this is the best solution, but this was the easiest.

Maybe the CONFIG_PARANOID_GENERIC_TIME should be added in the warnings
in init/main.c too?

Since interrupts are kept off in the ktimer (hrtimer, whatever) in
printk, this does not affect those patches. This is a PREEMPT_RT only
problem.

-- Steve

Index: linux-2.6.14-rt22/kernel/printk.c
===================================================================
--- linux-2.6.14-rt22.orig/kernel/printk.c 2005-12-06 21:44:53.000000000 -0500
+++ linux-2.6.14-rt22/kernel/printk.c 2005-12-06 21:52:11.000000000 -0500
@@ -757,7 +757,8 @@
* on PREEMPT_RT, call console drivers with
* interrupts enabled (unless we are debugging):
*/
-#if defined(CONFIG_PREEMPT_RT) && !defined(CONFIG_PRINTK_IGNORE_LOGLEVEL) && !defined(CONFIG_PPC)
+#if defined(CONFIG_PREEMPT_RT) && !defined(CONFIG_PRINTK_IGNORE_LOGLEVEL) && !defined(CONFIG_PPC) \
+ && !defined(CONFIG_PARANOID_GENERIC_TIME)
spin_unlock_irq(&logbuf_lock);
#else
spin_unlock(&logbuf_lock);

-
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