devres: provide devm_kstrdup_const()

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 33 insertions, 0 deletions

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index 438c91a43508..4aaf00d2098b 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 {
@@ -823,6 +825,28 @@ 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_GPL(devm_kstrdup_const);
+
+/**
  * devm_kvasprintf - Allocate resource managed space and format a string
  *                   into that.
  * @dev: Device to allocate memory for
@@ -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 c2022c1daef6..fecd9722400e 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -696,6 +696,8 @@ 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);