linux-kernel - [PATCH 3.12 043/127] drm/exynos: fix error handling in exynos_drm_subdrv

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Message-Id: <77b4c57fbe7ea2fbc337040b511cad340ffbf058.1480062521.git.jslaby@suse.cz>
Date:   Fri, 25 Nov 2016 09:29:16 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Inki Dae <inki.dae@...sung.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 043/127] drm/exynos: fix error handling in exynos_drm_subdrv_open

From: Arnd Bergmann <arnd@...db.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 55c4b906aa2aec3fa66310ec03c6842e34a04b2a upstream.

gcc-6 warns about a pointless loop in exynos_drm_subdrv_open:

drivers/gpu/drm/exynos/exynos_drm_core.c: In function 'exynos_drm_subdrv_open':
drivers/gpu/drm/exynos/exynos_drm_core.c:104:199: error: self-comparison always evaluates to false [-Werror=tautological-compare]
  list_for_each_entry_reverse(subdrv, &subdrv->list, list) {

Here, the list_for_each_entry_reverse immediately terminates because
the subdrv pointer is compared to itself as the loop end condition.

If we were to take the current subdrv pointer as the start of the
list (as we would do if list_for_each_entry_reverse() was not a macro),
we would iterate backwards over the &exynos_drm_subdrv_list anchor,
which would be even worse.

Instead, we need to use list_for_each_entry_continue_reverse()
to go back over each subdrv that was successfully opened until
the first entry.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Inki Dae <inki.dae@...sung.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/gpu/drm/exynos/exynos_drm_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_core.c b/drivers/gpu/drm/exynos/exynos_drm_core.c
index 1bef6dc77478..6d521497e3b4 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_core.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_core.c
@@ -204,7 +204,7 @@ int exynos_drm_subdrv_open(struct drm_device *dev, struct drm_file *file)
 	return 0;
 
 err:
-	list_for_each_entry_reverse(subdrv, &subdrv->list, list) {
+	list_for_each_entry_continue_reverse(subdrv, &exynos_drm_subdrv_list, list) {
 		if (subdrv->close)
 			subdrv->close(dev, subdrv->dev, file);
 	}
-- 
2.10.2