Re: [PATCH] Real-Time Preemption V0.7.52-07: rt_init_MUTEX_LOCKED declaration

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 2005-08-01 at 16:26 +0000, Luca Falavigna wrote:
> This patch fixes broken rt_init_MUTEX_LOCKED declaration using rt_sema_init()
> macro. This way we fix a potential compile bug: rt_init_MUTEX_LOCKED calls
> there_is_no_init_MUTEX_LOCKED_for_RT_semaphores, which is not referenced.
> (e.g. drivers/char/watchdog/cpu5wdt.c: "cpu5wdt: Unknown symbol
> there_is_no_init_MUTEX_LOCKED_for_RT_semaphores")
> 
> 

Ingo,

When did you solve the problem of ownership of locked semaphores? ;-)

Luca,
Unless Ingo did solve the problem of semaphores that can be locked by
one task and unlocked by another task, I wouldn't use your patch.
There's a problem with priority inheritance when it comes to these
semaphores.  That is who owns a locked semaphore that will later be
unlocked by someone else?  When a RT process blocks on this semaphore,
who does it boost to release it?  Ingo purposely put this in to crash
the compile so that we know where this can be a problem right away.

The patch you wanted to send was:

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Index: linux_realtime_ernie/drivers/char/watchdog/cpu5wdt.c
===================================================================
--- linux_realtime_ernie/drivers/char/watchdog/cpu5wdt.c	(revision 265)
+++ linux_realtime_ernie/drivers/char/watchdog/cpu5wdt.c	(working copy)
@@ -56,7 +56,7 @@
 /* some device data */
 
 static struct {
-	struct semaphore stop;
+	struct compat_semaphore stop;
 	volatile int running;
 	struct timer_list timer;
 	volatile int queue;