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Subject[PATCH][2.5] flush_tlb_all is not preempt safe.
Hi,
Considering that smp_call_function isn't allowed to hold a lock
reference and within smp_call_function we lock and unlock call_lock thus
triggering a preempt point. Therefore we can't guarantee that we'll be on
the same processor when we hit do_flush_tlb_all_local.

void flush_tlb_all(void)
{
preempt_disable();
smp_call_function (flush_tlb_all_ipi,0,1,1);

do_flush_tlb_all_local();
preempt_enable();
}

...

smp_call_function()
{
spin_lock(call_lock);
...
spin_unlock(call_lock);
<preemption point>
}

...

do_flush_tlb_all_local() - possibly not executing on same processor
anymore.

This case is fixed in my smp_call_function_on_cpu patches by not allowing
smp_call_function to invoke preemption.

Index: linux-2.5.60-uml/arch/i386/kernel/smp.c
===================================================================
RCS file: /build/cvsroot/linux-2.5.60/arch/i386/kernel/smp.c,v
retrieving revision 1.1.1.1
diff -u -r1.1.1.1 smp.c
--- linux-2.5.60-uml/arch/i386/kernel/smp.c 10 Feb 2003 22:14:16 -0000 1.1.1.1
+++ linux-2.5.60-uml/arch/i386/kernel/smp.c 14 Feb 2003 10:59:19 -0000
@@ -452,9 +452,11 @@

void flush_tlb_all(void)
{
+ preempt_disable();
smp_call_function (flush_tlb_all_ipi,0,1,1);

do_flush_tlb_all_local();
+ preempt_enable();
}

/*
--
function.linuxpower.ca
-
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