efi_pstore: Introducing workqueue updating sysfs

commit a93bc0c6e07ed9bac44700280e65e2945d864fd4 upstream.

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

[Patch Description]
This patch removes sysfs operations from a write callback by introducing
a workqueue updating sysfs entries which is scheduled after the write
callback is called.

Also, the workqueue is kicked in a just oops case.
A system will go down in other cases such as panic, clean shutdown and emergency
restart. And we don't need to create sysfs entries because there is no chance for
users to access to them.

efi_pstore will be robust against a kernel panic in an interrupt context with this patch.

Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
[xr: Backported to 3.4:
  - Adjust contest
  - Remove repeated definition of helper function variable_is_present]
Signed-off-by: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index c3a2f6f11748215cb9784110c186017c2e2653b1..3161dd3f700a80b58e4ce373d4d0a8a743e9e588 100644 (file)
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -154,6 +154,13 @@ 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_entries(struct work_struct *);
+static DECLARE_WORK(efivar_work, efivar_update_sysfs_entries);
+
 /* Return the number of unicode characters in data */
 static unsigned long
 utf16_strnlen(efi_char16_t *s, size_t maxlength)
@@ -839,11 +846,8 @@ static int efi_pstore_write(enum pstore_type_id type,
        if (found)
                efivar_unregister(found);
 
-       if (size)
-               ret = efivar_create_sysfs_entry(efivars,
-                                         utf16_strsize(efi_name,
-                                                       DUMP_NAME_LEN * 2),
-                                         efi_name, &vendor);
+       if (reason == KMSG_DUMP_OOPS)
+               schedule_work(&efivar_work);
 
        *id = part;
        return ret;
@@ -1044,6 +1048,53 @@ static bool variable_is_present(efi_char16_t *variable_name, efi_guid_t *vendor)
        return found;
 }
 
+static void efivar_update_sysfs_entries(struct work_struct *work)
+{
+       struct efivars *efivars = &__efivars;
+       efi_guid_t vendor;
+       efi_char16_t *variable_name;
+       unsigned long variable_name_size = 1024;
+       efi_status_t status = EFI_NOT_FOUND;
+       bool found;
+
+       /* 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_irq(&efivars->lock);
+               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_irq(&efivars->lock);
+
+               if (!found) {
+                       kfree(variable_name);
+                       break;
+               } else
+                       efivar_create_sysfs_entry(efivars,
+                                                 variable_name_size,
+                                                 variable_name, &vendor);
+       }
+}
+
 /*
  * Returns the size of variable_name, in bytes, including the
  * terminating NULL character, or variable_name_size if no NULL

diff --git a/include/linux/efi.h b/include/linux/efi.h
index 260b2c5cb4cbd4cc60d942673c9b10371015f049..9b69e479421dc82dcea316a12f093c0381ccf4b0 100644 (file)
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -666,7 +666,8 @@ 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_entries(),
         * which is protected by the BKL, so that path is safe.
         */
        spinlock_t lock;