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;