[PATCH] ACPI / extlog: don't dereference extlog_l1_addr if it is null

[Colin King <colin.king@canonical.com>]

From: Colin Ian King <colin.king@canonical.com>

There is a check to see if extlog_l1_addr is null before calling
acpi_os_unmap_iomem, however, before that call there is a
dereference on this that could trip an oops.  Move the
extlog_l1_addr dereference so it occurs only if it is not null.

Found by static analysis by smatch.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/acpi/acpi_extlog.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/acpi_extlog.c b/drivers/acpi/acpi_extlog.c
index b3842ff..183b7b2 100644
--- a/drivers/acpi/acpi_extlog.c
+++ b/drivers/acpi/acpi_extlog.c
@@ -309,9 +309,10 @@ static void __exit extlog_exit(void)
 {
 	set_edac_report_status(old_edac_report_status);
 	mce_unregister_decode_chain(&extlog_mce_dec);
-	((struct extlog_l1_head *)extlog_l1_addr)->flags &= ~FLAG_OS_OPTIN;
-	if (extlog_l1_addr)
+	if (extlog_l1_addr) {
+		((struct extlog_l1_head *)extlog_l1_addr)->flags &= ~FLAG_OS_OPTIN;
 		acpi_os_unmap_iomem(extlog_l1_addr, l1_size);
+	}
 	if (elog_addr)
 		acpi_os_unmap_iomem(elog_addr, elog_size);
 	release_mem_region(elog_base, elog_size);
-- 
2.6.2