Re: [PATCH] net: iptables: rework the fix of xt_info locking

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

On Wed, Mar 02, 2011 at 05:14:14PM -0300, Luis Claudio R. Goncalves wrote:
> Thomas,
> 
> Maybe PREEMPT_NONE is not really what we want to check against, maybe it is 
> RT_MUTEXES... anyway, this patch works fine as is in kernels with
> PREEMPT_NONE, PREEMPT_DESKTOP, PREEMPT_VOLUNTARY and PREEMPT_RT set.
> 
> ---
> 
> net: iptables: rework the fix of xt_info locking
> 
> Commit 5bbbedc from tip/rt/2.6.33 fixed an annoying locking issue on
> PREEMPT_RT enabled kernels. I have observed a similar issue when testing a
> kernel with PREEMPT_DESKTOP enabled. My test kernels would boot fine and as
> soon as I tried to ssh into the test box I would see messages like this one:
> 
> 	BUG: %Ps exited with wrong preemption count!
> 	=> enter: 00000101, exit: 00000100.
> 	BUG: %Ps exited with wrong preemption count!
> 	=> enter: 00000101, exit: 00000100.
> 	BUG: %Ps exited with wrong preemption count!
> 	=> enter: 00000102, exit: 00000101.

This error message would be a bit more usful after this patch:

diff --git a/kernel/softirq.c b/kernel/softirq.c
index c35f72b..b3b20b0 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -335,8 +335,8 @@ debug_check_preempt_count_stop(__u32 *preempt_count, struct softirq_action *h)
 	if (*preempt_count == preempt_count())
 		return;
 
-	print_symbol("BUG: %Ps exited with wrong preemption count!\n",
-		     (unsigned long)h->action);
+	printk("BUG: %ps exited with wrong preemption count!\n",
+			h->action);
 	printk("=> enter: %08x, exit: %08x.\n", *preempt_count, preempt_count());
 	preempt_count() = *preempt_count;
 #endif

Note this is completely untested and applies on top of v2.6.33.7.2-rt30.

Thomas: should I send a proper patch or isn't it worth the effort?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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