devres: provide devm_krealloc()

Implement the managed variant of krealloc(). This function works with
all memory allocated by devm_kmalloc() (or devres functions using it
implicitly like devm_kmemdup(), devm_kstrdup() etc.).

Managed realloc'ed chunks can be manually released with devm_kfree().

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200824173859.4910-2-brgl@bgdev.pl
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/driver-model/devres.rst

@@ -354,6 +354,7 @@ MEM
   devm_kmalloc()
   devm_kmalloc_array()
   devm_kmemdup()
+  devm_krealloc()
   devm_kstrdup()
   devm_kvasprintf()
   devm_kzalloc()

drivers/base/devres.c

@@ -126,6 +126,14 @@ static void add_dr(struct device *dev, struct devres_node *node)
 	list_add_tail(&node->entry, &dev->devres_head);
 }
 
+static void replace_dr(struct device *dev,
+		       struct devres_node *old, struct devres_node *new)
+{
+	devres_log(dev, old, "REPLACE");
+	BUG_ON(!list_empty(&new->entry));
+	list_replace(&old->entry, &new->entry);
+}
+
 #ifdef CONFIG_DEBUG_DEVRES
 void * __devres_alloc_node(dr_release_t release, size_t size, gfp_t gfp, int nid,
 		      const char *name)
@@ -837,6 +845,103 @@ void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp)
 }
 EXPORT_SYMBOL_GPL(devm_kmalloc);
 
+/**
+ * devm_krealloc - Resource-managed krealloc()
+ * @dev: Device to re-allocate memory for
+ * @ptr: Pointer to the memory chunk to re-allocate
+ * @new_size: New allocation size
+ * @gfp: Allocation gfp flags
+ *
+ * Managed krealloc(). Resizes the memory chunk allocated with devm_kmalloc().
+ * Behaves similarly to regular krealloc(): if @ptr is NULL or ZERO_SIZE_PTR,
+ * it's the equivalent of devm_kmalloc(). If new_size is zero, it frees the
+ * previously allocated memory and returns ZERO_SIZE_PTR. This function doesn't
+ * change the order in which the release callback for the re-alloc'ed devres
+ * will be called (except when falling back to devm_kmalloc() or when freeing
+ * resources when new_size is zero). The contents of the memory are preserved
+ * up to the lesser of new and old sizes.
+ */
+void *devm_krealloc(struct device *dev, void *ptr, size_t new_size, gfp_t gfp)
+{
+	size_t total_new_size, total_old_size;
+	struct devres *old_dr, *new_dr;
+	unsigned long flags;
+
+	if (unlikely(!new_size)) {
+		devm_kfree(dev, ptr);
+		return ZERO_SIZE_PTR;
+	}
+
+	if (unlikely(ZERO_OR_NULL_PTR(ptr)))
+		return devm_kmalloc(dev, new_size, gfp);
+
+	if (WARN_ON(is_kernel_rodata((unsigned long)ptr)))
+		/*
+		 * We cannot reliably realloc a const string returned by
+		 * devm_kstrdup_const().
+		 */
+		return NULL;
+
+	if (!check_dr_size(new_size, &total_new_size))
+		return NULL;
+
+	total_old_size = ksize(container_of(ptr, struct devres, data));
+	if (total_old_size == 0) {
+		WARN(1, "Pointer doesn't point to dynamically allocated memory.");
+		return NULL;
+	}
+
+	/*
+	 * If new size is smaller or equal to the actual number of bytes
+	 * allocated previously - just return the same pointer.
+	 */
+	if (total_new_size <= total_old_size)
+		return ptr;
+
+	/*
+	 * Otherwise: allocate new, larger chunk. We need to allocate before
+	 * taking the lock as most probably the caller uses GFP_KERNEL.
+	 */
+	new_dr = alloc_dr(devm_kmalloc_release,
+			  total_new_size, gfp, dev_to_node(dev));
+	if (!new_dr)
+		return NULL;
+
+	/*
+	 * The spinlock protects the linked list against concurrent
+	 * modifications but not the resource itself.
+	 */
+	spin_lock_irqsave(&dev->devres_lock, flags);
+
+	old_dr = find_dr(dev, devm_kmalloc_release, devm_kmalloc_match, ptr);
+	if (!old_dr) {
+		spin_unlock_irqrestore(&dev->devres_lock, flags);
+		kfree(new_dr);
+		WARN(1, "Memory chunk not managed or managed by a different device.");
+		return NULL;
+	}
+
+	replace_dr(dev, &old_dr->node, &new_dr->node);
+
+	spin_unlock_irqrestore(&dev->devres_lock, flags);
+
+	/*
+	 * We can copy the memory contents after releasing the lock as we're
+	 * no longer modyfing the list links.
+	 */
+	memcpy(new_dr->data, old_dr->data,
+	       total_old_size - offsetof(struct devres, data));
+	/*
+	 * Same for releasing the old devres - it's now been removed from the
+	 * list. This is also the reason why we must not use devm_kfree() - the
+	 * links are no longer valid.
+	 */
+	kfree(old_dr);
+
+	return new_dr->data;
+}
+EXPORT_SYMBOL_GPL(devm_krealloc);
+
 /**
  * devm_kstrdup - Allocate resource managed space and
  *                copy an existing string into that.

include/linux/device.h

@@ -206,6 +206,8 @@ int devres_release_group(struct device *dev, void *id);
 
 /* managed devm_k.alloc/kfree for device drivers */
 void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) __malloc;
+void *devm_krealloc(struct device *dev, void *ptr, size_t size,
+		    gfp_t gfp) __must_check;
 __printf(3, 0) char *devm_kvasprintf(struct device *dev, gfp_t gfp,
 				     const char *fmt, va_list ap) __malloc;
 __printf(3, 4) char *devm_kasprintf(struct device *dev, gfp_t gfp,