[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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