linux-kernel - [PATCH] drm/omap: dss: do not allow devm

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Message-Id: <1542974495-12387-1-git-send-email-hofrat@osadl.org>
Date:   Fri, 23 Nov 2018 13:01:35 +0100
From:   Nicholas Mc Guire <hofrat@...dl.org>
To:     Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     David Airlie <airlied@...ux.ie>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sebastian Reichel <sre@...nel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        "Andrew F. Davis" <afd@...com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH] drm/omap: dss: do not allow devm_kasprintf() to fail

omapdss_display_init() is called by multiple drivers and does not expect
a return value so without changing all call-sites the low-probability
failure of devm_kasprintf() can not be reported up the call stack. As
the amount allocated here is very small (<= 16 bytes) and it is an
initialization function that most likely will be called during system
initialization it should be OK to use __GFP_NOFAIL here to prevent
devm_kasprintf() from returning NULL.

Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
Fixes: 36c61ae2b755 ("drm/omap: dss: Remove display ordering from dss/display.c")
---

Problem located with experimental coccinelle script

While the use of __GFP_NOFAIL is to be limited (small infrequent 
allocations) this case does seems suitable as it is rare and small
(initialization) .As all the current drivers using 
omapdss_display_init() currently seem not to initialize dssdev->name
prior to calling omapdss_display_init() and the unlikely failure
case can not be reasonably responded (returns void) not allowing
a allocation failure here should be acceptable.

Patch was compile tested with: omap2plus_defconfig (implies OMAP_DSS_BASE=m)

Patch is against 4.20-rc3 (localversion-next is next-20181123)

 drivers/gpu/drm/omapdrm/dss/display.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/display.c b/drivers/gpu/drm/omapdrm/dss/display.c
index 34b2a4e..7dbe874 100644
--- a/drivers/gpu/drm/omapdrm/dss/display.c
+++ b/drivers/gpu/drm/omapdrm/dss/display.c
@@ -45,7 +45,8 @@ void omapdss_display_init(struct omap_dss_device *dssdev)
 	of_property_read_string(dssdev->dev->of_node, "label", &dssdev->name);

 	if (dssdev->name == NULL)
-		dssdev->name = devm_kasprintf(dssdev->dev, GFP_KERNEL,
+		dssdev->name = devm_kasprintf(dssdev->dev,
+					      GFP_KERNEL | __GFP_NOFAIL,
 					      "display%u", id);
 }
 EXPORT_SYMBOL_GPL(omapdss_display_init);
-- 
2.1.4