del_timer_sync needed for UP RT systems.

From: George Anzinger
Date: Tue Apr 26 2005 - 18:48:02 EST


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@xxxxxxxxxx
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