[PATCH AUTOSEL 6.6 07/14] ACPI: extlog: fix NULL pointer dereference check

[Sasha Levin <sashal@xxxxxxxxxx>]

From: Prarit Bhargava <prarit@xxxxxxxxxx>

[ Upstream commit 72d9b9747e78979510e9aafdd32eb99c7aa30dd1 ]

The gcc plugin -fanalyzer [1] tries to detect various
patterns of incorrect behaviour.  The tool reports:

drivers/acpi/acpi_extlog.c: In function ‘extlog_exit’:
drivers/acpi/acpi_extlog.c:307:12: warning: check of ‘extlog_l1_addr’ for NULL after already dereferencing it [-Wanalyzer-deref-before-check]
    |
    |  306 |         ((struct extlog_l1_head *)extlog_l1_addr)->flags &= ~FLAG_OS_OPTIN;
    |      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
    |      |                                                  |
    |      |                                                  (1) pointer ‘extlog_l1_addr’ is dereferenced here
    |  307 |         if (extlog_l1_addr)
    |      |            ~
    |      |            |
    |      |            (2) pointer ‘extlog_l1_addr’ is checked for NULL here but it was already dereferenced at (1)
    |

Fix the NULL pointer dereference check in extlog_exit().

Link: https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Static-Analyzer-Options.html # [1]

Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 e120a96e1eae..193147769146 100644
--- a/drivers/acpi/acpi_extlog.c
+++ b/drivers/acpi/acpi_extlog.c
@@ -303,9 +303,10 @@ static int __init extlog_init(void)
 static void __exit extlog_exit(void)
 {
 	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);
-- 
2.43.0