[RESEND PATCH v6 3/4] devres: provide devm_kstrdup_const()

Bartosz Golaszewski
2018-10-14T15:20:26Z

Provide a resource managed version of kstrdup_const(). This variant
internally calls devm_kstrdup() on pointers that are outside of
.rodata section and returns the string as is otherwise.

Make devm_kfree() check if the passed pointer doesn't point to .rodata
and if so - don't actually destroy the resource.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
drivers/base/devres.c | 31 +++++++++++++++++++++++++++++++
include/linux/device.h | 2 ++
2 files changed, 33 insertions(+)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index 438c91a43508..00c70f0fcdcd 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -11,6 +11,8 @@
#include <linux/slab.h>
#include <linux/percpu.h>

+#include <asm/sections.h>
+
#include "base.h"

struct devres_node {
@@ -822,6 +824,28 @@ char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp)
}
EXPORT_SYMBOL_GPL(devm_kstrdup);

+/**
+ * devm_kstrdup_const - resource managed conditional string duplication
+ * @dev: device for which to duplicate the string
+ * @s: the string to duplicate
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ *
+ * Strings allocated by devm_kstrdup_const will be automatically freed when
+ * the associated device is detached.
+ *
+ * RETURNS:
+ * Source string if it is in .rodata section otherwise it falls back to
+ * devm_kstrdup.
+ */
+const char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
+{
+ if (is_kernel_rodata((unsigned long)s))
+ return s;
+
+ return devm_kstrdup(dev, s, gfp);
+}
+EXPORT_SYMBOL(devm_kstrdup_const);
+
/**
* devm_kvasprintf - Allocate resource managed space and format a string
* into that.
@@ -889,6 +913,13 @@ void devm_kfree(struct device *dev, const void *p)
{
int rc;

+ /*
+ * Special case: pointer to a string in .rodata returned by
+ * devm_kstrdup_const().
+ */
+ if (unlikely(is_kernel_rodata((unsigned long)p)))
+ return;
+
rc = devres_destroy(dev, devm_kmalloc_release,
devm_kmalloc_match, (void *)p);
WARN_ON(rc);
diff --git a/include/linux/device.h b/include/linux/device.h
index 33f7cb271fbb..e626acb93ef5 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -694,6 +694,8 @@ static inline void *devm_kcalloc(struct device *dev,
}
extern void devm_kfree(struct device *dev, const void *p);
extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
+extern const char *devm_kstrdup_const(struct device *dev,
+ const char *s, gfp_t gfp);
extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
gfp_t gfp);

--
2.19.1