flush_tlb_mm() bug fix

The flush_tlb_mm() routine contained a long-standing bug back from the days when SMP support was added to ia64 linux. It causes seemingly random and temporary memory "corruption" when a multi-threaded task does a fork() on an SMP machine. Note that both a conditions are
required: the bug doesn't trigger on UP machines or when fork() is called from a single-threaded program. Fortunately, there don't seem to be all that many programs doing that (OK, if there were more programs doing that, we would have found the bug earlier...).

A quick patch is below (for the 2.5 tree, 2.4 quick fix is analogous, except that the change needs to be made in pgalloc.h:flush_tlb_mm()). A cleaner and (supposedly) better-performing fix is in the 2.5 bitkeeper tree:

	http://lia64.bkbits.net:8080/to-linus-2.5/[email protected]

Thanks to Steve Goldman and Hans Boehm for helping to identify and track down the bug

Regards,

	--david

=== include/asm-ia64/tlbflush.h 1.3 vs edited ==--- 1.3/include/asm-ia64/tlbflush.h Fri Aug 9 17:16:44 2002
+++ edited/include/asm-ia64/tlbflush.h Wed Nov 13 11:47:37 2002
@@ -39,6 +39,11 @@
{
if (mm) {
mm->context = 0;
+#ifdef CONFIG_SMP
+ if (atomic_read(&mm->mm_users) > 1)
+ flush_tlb_all();
+ else
+#endif
if (mm = current->active_mm) {
/* This is called, e.g., as a result of exec(). */ get_new_mmu_context(mm);