linux-kernel - [PATCH 1/3] drm/i915: allocate mock file pointer dynamically

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Date:   Mon, 20 Mar 2017 10:40:27 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Matthew Auld <matthew.auld@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] drm/i915: allocate mock file pointer dynamically

A struct file is a bit too large to put on the kernel stack in general
and triggers a warning for low settings of CONFIG_FRAME_WARN:

drivers/gpu/drm/i915/selftests/mock_drm.c: In function 'mock_file':
drivers/gpu/drm/i915/selftests/mock_drm.c:46:1: error: the frame size of 1328 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
drivers/gpu/drm/i915/selftests/mock_drm.c: In function 'mock_file_free':
drivers/gpu/drm/i915/selftests/mock_drm.c:54:1: error: the frame size of 1312 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]

It's also slightly dangerous to leave a reference to a stack object
in the drm_file structure after leaving the stack frame.
This changes the code to just allocate the object dynamically
and release it when we are done with it.

Fixes: 66d9cb5d805a ("drm/i915: Mock the GEM device for self-testing")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/i915/selftests/mock_drm.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/selftests/mock_drm.c b/drivers/gpu/drm/i915/selftests/mock_drm.c
index 113dec05c7dc..18514065c93d 100644
--- a/drivers/gpu/drm/i915/selftests/mock_drm.c
+++ b/drivers/gpu/drm/i915/selftests/mock_drm.c
@@ -32,15 +32,15 @@ static inline struct inode fake_inode(struct drm_i915_private *i915)
 struct drm_file *mock_file(struct drm_i915_private *i915)
 {
 	struct inode inode = fake_inode(i915);
-	struct file filp = {};
+	struct file *filp = kzalloc(sizeof(struct file), GFP_KERNEL);
 	struct drm_file *file;
 	int err;
 
-	err = drm_open(&inode, &filp);
+	err = drm_open(&inode, filp);
 	if (unlikely(err))
 		return ERR_PTR(err);
 
-	file = filp.private_data;
+	file = filp->private_data;
 	file->authenticated = true;
 	return file;
 }
@@ -48,7 +48,9 @@ struct drm_file *mock_file(struct drm_i915_private *i915)
 void mock_file_free(struct drm_i915_private *i915, struct drm_file *file)
 {
 	struct inode inode = fake_inode(i915);
-	struct file filp = { .private_data = file };
+	struct file *filp = file->filp;
 
-	drm_release(&inode, &filp);
+	drm_release(&inode, filp);
+
+	kfree(filp);
 }
-- 
2.9.0