Message-ID: <426ED1EC.80500@mvista.com>
Date: Tue, 26 Apr 2005 16:42:36 -0700
From: George Anzinger <george@mvista.com>
Reply-To: ganzinger@mvista.com
Organization: MontaVista Software
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To: ingo@mvista.com
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: del_timer_sync needed for UP  RT systems.
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Ingo,

In tracking down the failure of a system running the RT patch we have found a 
preemption between the time run_timer_list clears its spinlock and the call back 
function (in this case in posix-timers.c) gets its spinlock.  The bad news is 
that it is possible for the timer to be released at this point leaving the call 
back code with a pointer to a bogus timer.

This was/is possible, of course, in SMP systems and is why del_timer_sync() 
exists.  I suspect that del_timer_sync() needs to also do the "right thing" in 
UP RT systems.

This means removing the #ifdef CONFIG_SMP at about line 56 of kernel/timer.c 
thus setting up base->running_timer in all cases (or at least in SMP and RT 
cases) and also the #ifdef CONFIG_SMP around del_timer_sync() and, of course, 
the defines that redirect calls to these functions.

Does this make sense?
-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
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