1 files changed, 54 insertions, 7 deletions

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 5abe943e3404..70a0fb10517f 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -321,11 +321,11 @@ static unsigned long var_name_strnsize(efi_char16_t *variable_name,
  * Print a warning when duplicate EFI variables are encountered and
  * disable the sysfs workqueue since the firmware is buggy.
  */
-static void dup_variable_bug(efi_char16_t *s16, efi_guid_t *vendor_guid,
+static void dup_variable_bug(efi_char16_t *str16, efi_guid_t *vendor_guid,
 			     unsigned long len16)
 {
 	size_t i, len8 = len16 / sizeof(efi_char16_t);
-	char *s8;
+	char *str8;
 
 	/*
 	 * Disable the workqueue since the algorithm it uses for
@@ -334,16 +334,16 @@ static void dup_variable_bug(efi_char16_t *s16, efi_guid_t *vendor_guid,
 	 */
 	efivar_wq_enabled = false;
 
-	s8 = kzalloc(len8, GFP_KERNEL);
-	if (!s8)
+	str8 = kzalloc(len8, GFP_KERNEL);
+	if (!str8)
 		return;
 
 	for (i = 0; i < len8; i++)
-		s8[i] = s16[i];
+		str8[i] = str16[i];
 
 	printk(KERN_WARNING "efivars: duplicate variable: %s-%pUl\n",
-	       s8, vendor_guid);
-	kfree(s8);
+	       str8, vendor_guid);
+	kfree(str8);
 }
 
 /**
@@ -595,6 +595,39 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
 }
 EXPORT_SYMBOL_GPL(efivar_entry_set);
 
+/*
+ * efivar_entry_set_nonblocking - call set_variable_nonblocking()
+ *
+ * This function is guaranteed to not block and is suitable for calling
+ * from crash/panic handlers.
+ *
+ * Crucially, this function will not block if it cannot acquire
+ * __efivars->lock. Instead, it returns -EBUSY.
+ */
+static int
+efivar_entry_set_nonblocking(efi_char16_t *name, efi_guid_t vendor,
+			     u32 attributes, unsigned long size, void *data)
+{
+	const struct efivar_operations *ops = __efivars->ops;
+	unsigned long flags;
+	efi_status_t status;
+
+	if (!spin_trylock_irqsave(&__efivars->lock, flags))
+		return -EBUSY;
+
+	status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
+	if (status != EFI_SUCCESS) {
+		spin_unlock_irqrestore(&__efivars->lock, flags);
+		return -ENOSPC;
+	}
+
+	status = ops->set_variable_nonblocking(name, &vendor, attributes,
+					       size, data);
+
+	spin_unlock_irqrestore(&__efivars->lock, flags);
+	return efi_status_to_err(status);
+}
+
 /**
  * efivar_entry_set_safe - call set_variable() if enough space in firmware
  * @name: buffer containing the variable name
@@ -622,6 +655,20 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 	if (!ops->query_variable_store)
 		return -ENOSYS;
 
+	/*
+	 * If the EFI variable backend provides a non-blocking
+	 * ->set_variable() operation and we're in a context where we
+	 * cannot block, then we need to use it to avoid live-locks,
+	 * since the implication is that the regular ->set_variable()
+	 * will block.
+	 *
+	 * If no ->set_variable_nonblocking() is provided then
+	 * ->set_variable() is assumed to be non-blocking.
+	 */
+	if (!block && ops->set_variable_nonblocking)
+		return efivar_entry_set_nonblocking(name, vendor, attributes,
+						    size, data);
+
 	if (!block) {
 		if (!spin_trylock_irqsave(&__efivars->lock, flags))
 			return -EBUSY;