ACPI, APEI, Fix acpi_pre_map() return value

After we ioremap() a new region, we call __acpi_try_ioremap() to
see whether another thread has already mapped the same region.
This check clobbers "vaddr",  so compute the return value of
acpi_pre_map() using the ioremap() result "map->vaddr" instead.

v2:
    Modified the unsuitable description of patch.

v3:
    Removed unlikely() check and made description simpler.

Signed-off-by: Jin Dongming <[email protected]>
Reviewed-by: Andi Kleen <[email protected]>
Signed-off-by: Huang Ying <[email protected]>
Signed-off-by: Len Brown <[email protected]>

drivers/acpi/atomicio.c

@@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 	list_add_tail_rcu(&map->list, &acpi_iomaps);
 	spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 
-	return vaddr + (paddr - pg_off);
+	return map->vaddr + (paddr - map->paddr);
 err_unmap:
 	iounmap(vaddr);
 	return NULL;