[RESEND][PATCH v4 2/3] efi_pstore: Introducing workqueue updatingsysfs entries

[Seiji Aguchi]

[Problem]
  efi_pstore creates sysfs entries ,which enable users to access to NVRAM,
  in a write callback. If a kernel panic happens in interrupt contexts, pstore may
  fail because it could sleep due to dynamic memory allocations during creating sysfs entries.

[Patch Description]
 This patch removes sysfs operations from write callback by introducing a workqueue
 updating sysfs entries which is kicked after a write callback of efi_pstore is called.
 efi_pstore will be robust against a kernel panic in an interrupt context with it.
 The workqueue works as follows.

 - A timer is registered during an initialization of efivars module.
 - A flag, update_sysfs_entries, is checked periodically with the timer.
 - The flag is set in a write callback, efi_pstore_write().
 - Operation updating sysfs entries is kicked if the flag is set.

 Any operations ,like registering a timer, are not added in a write callback because it may run
 in panic case and fail due to operations related to workqueue.

 To make efi_pstore work in panic case, a write callback should just log to NVRAM.

Signed-off-by: Seiji Aguchi <seiji.aguchi@xxxxxxx>
---
 drivers/firmware/efivars.c |  119 +++++++++++++++++++++++++++++++++++++++----
 include/linux/efi.h        |    3 +-
 2 files changed, 110 insertions(+), 12 deletions(-)

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index bd1df01..cd16ea6 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -146,6 +146,13 @@ efivar_create_sysfs_entry(struct efivars *efivars,
 			  efi_char16_t *variable_name,
 			  efi_guid_t *vendor_guid);
 
+/*
+ * Prototype for workqueue functions updating sysfs entry
+ */
+
+static void efivar_update_sysfs_entry(struct work_struct *);
+static DECLARE_WORK(efivar_work, efivar_update_sysfs_entry);
+
 /* Return the number of unicode characters in data */
 static unsigned long
 utf16_strnlen(efi_char16_t *s, size_t maxlength)
@@ -731,9 +738,6 @@ static int efi_pstore_write(enum pstore_type_id type,
 					   0, NULL);
 	}
 
-	if (found)
-		list_del(&found->list);
-
 	for (i = 0; i < DUMP_NAME_LEN; i++)
 		efi_name[i] = name[i];
 
@@ -742,14 +746,7 @@ static int efi_pstore_write(enum pstore_type_id type,
 
 	spin_unlock_irqrestore(&efivars->lock, flags);
 
-	if (found)
-		efivar_unregister(found);
-
-	if (size)
-		ret = efivar_create_sysfs_entry(efivars,
-					  utf16_strsize(efi_name,
-							DUMP_NAME_LEN * 2),
-					  efi_name, &vendor);
+	schedule_work(&efivar_work);
 
 	*id = part;
 	return ret;
@@ -1200,6 +1197,104 @@ EXPORT_SYMBOL_GPL(register_efivars);
 static struct efivars __efivars;
 static struct efivar_operations ops;
 
+static void delete_all_stale_sysfs_entries(void)
+{
+	struct efivars *efivars = &__efivars;
+	struct efivar_entry *entry, *n, *found;
+	efi_status_t status;
+	unsigned long flags;
+
+	while (1) {
+		found = NULL;
+		spin_lock_irqsave(&efivars->lock, flags);
+		list_for_each_entry_safe(entry, n, &efivars->list, list) {
+			status = get_var_data_locked(efivars, &entry->var);
+			if (status != EFI_SUCCESS) {
+				found = entry;
+				list_del(&entry->list);
+				break;
+			}
+		}
+		spin_unlock_irqrestore(&efivars->lock, flags);
+		if (found)
+			efivar_unregister(entry);
+		else
+			break;
+	}
+}
+
+static bool variable_is_present(efi_char16_t *variable_name, efi_guid_t *vendor)
+{
+	struct efivar_entry *entry, *n;
+	struct efivars *efivars = &__efivars;
+	unsigned long strsize1, strsize2;
+	bool found = false;
+
+	strsize1 = utf16_strsize(variable_name, 1024);
+	list_for_each_entry_safe(entry, n, &efivars->list, list) {
+		strsize2 = utf16_strsize(entry->var.VariableName, 1024);
+		if (strsize1 == strsize2 &&
+			!memcmp(variable_name, &(entry->var.VariableName),
+				strsize2) &&
+			!efi_guidcmp(entry->var.VendorGuid,
+				*vendor)) {
+			found = true;
+			break;
+		}
+	}
+	return found;
+}
+
+static void efivar_update_sysfs_entry(struct work_struct *work)
+{
+	struct efivars *efivars = &__efivars;
+	efi_guid_t vendor;
+	efi_char16_t *variable_name;
+	unsigned long variable_name_size = 1024, flags;
+	efi_status_t status = EFI_NOT_FOUND;
+	bool found;
+
+	/* Delete stale sysfs entries */
+	delete_all_stale_sysfs_entries();
+
+	/* Add new sysfs entries */
+	while (1) {
+		variable_name = kzalloc(variable_name_size, GFP_KERNEL);
+		if (!variable_name) {
+			pr_err("efivars: Memory allocation failed.\n");
+			return;
+		}
+
+		spin_lock_irqsave(&efivars->lock, flags);
+		found = false;
+		while (1) {
+			variable_name_size = 1024;
+			status = efivars->ops->get_next_variable(
+							&variable_name_size,
+							variable_name,
+							&vendor);
+			if (status != EFI_SUCCESS) {
+				break;
+			} else {
+				if (!variable_is_present(variable_name,
+				    &vendor)) {
+					found = true;
+					break;
+				}
+			}
+		}
+		spin_unlock_irqrestore(&efivars->lock, flags);
+
+		if (!found) {
+			kfree(variable_name);
+			break;
+		} else
+			efivar_create_sysfs_entry(efivars,
+						  variable_name_size,
+						  variable_name, &vendor);
+	}
+}
+
 /*
  * For now we register the efi subsystem with the firmware subsystem
  * and the vars subsystem with the efi subsystem.  In the future, it
@@ -1254,6 +1349,8 @@ err_put:
 static void __exit
 efivars_exit(void)
 {
+	cancel_work_sync(&efivar_work);
+
 	if (efi_enabled) {
 		unregister_efivars(&__efivars);
 		kobject_put(efi_kobj);
diff --git a/include/linux/efi.h b/include/linux/efi.h
index ec45ccd..8e03cc0 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -643,7 +643,8 @@ struct efivars {
 	 * 1) ->list - adds, removals, reads, writes
 	 * 2) ops.[gs]et_variable() calls.
 	 * It must not be held when creating sysfs entries or calling kmalloc.
-	 * ops.get_next_variable() is only called from register_efivars(),
+	 * ops.get_next_variable() is only called from register_efivars()
+	 * or efivar_update_sysfs_entry(),
 	 * which is protected by the BKL, so that path is safe.
 	 */
 	spinlock_t lock;
-- 
1.7.1
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