[Dle-develop] [RFC][PATCH v2 3/3] efi_pstore: Skip scheduling a workqueue in cases other than oops

[Seiji A. <sei...@hd...>]

[Problem]
efi_pstore creates sysfs files when logging kernel messages to NVRAM.
Currently, the sysfs files are updated in a workqueue which is registered in a write callback.

On the other hand, a situation which users need the sysfs files is just oops case because a system will 
be down and they can't access to sysfs files in other cases like panic, reboot or emergency_restart.

Also, if kernel panics due to a bug of workqueue operations and a write callback of efi_pstore is called in
panic case, efi_pstore may fail due to a failure of schedule_work(). 
And panic_notifier_chain()/emergency_restart() is not kicked if efi_pstore fails.  
This may cause user's unwanted result.

[Patch Description]
This patch skips a registration of a workqueue in a write callback in cases other than oops.

Also, a logic of erase callback is freshly created instead of sharing with a write callback because the sysfs 
operation is kicked in just oops case in a write callback and an erase callback doesn't work without any change.
By separating a logic to a write callback, an erase callback works correctly.

Signed-off-by: Seiji Aguchi <sei...@hd...>
---
 drivers/firmware/efivars.c |   53 ++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 8717ea9..4811abb 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -747,7 +747,11 @@ static int efi_pstore_write(enum pstore_type_id type,
 
 	spin_unlock_irqrestore(&efivars->lock, flags);
 
-	schedule_work(&efivar_work);
+	/*
+	 * The user may want to see an entry for this write in sysfs.
+	 */
+	if (reason == KMSG_DUMP_OOPS)
+		schedule_work(&efivar_work);
 
 	*id = part;
 	return ret;
@@ -756,7 +760,52 @@ static int efi_pstore_write(enum pstore_type_id type,
 static int efi_pstore_erase(enum pstore_type_id type, u64 id,
 			    struct pstore_info *psi)
 {
-	efi_pstore_write(type, 0, &id, (unsigned int)id, 0, psi);
+	char stub_name[DUMP_NAME_LEN];
+	efi_char16_t efi_name[DUMP_NAME_LEN];
+	efi_guid_t vendor = LINUX_EFI_CRASH_GUID;
+	struct efivars *efivars = psi->data;
+	struct efivar_entry *entry, *found = NULL;
+	int i;
+	unsigned long flags;
+
+	sprintf(stub_name, "dump-type%u-%llu-", type, id);
+
+	spin_lock_irqsave(&efivars->lock, flags);
+
+	for (i = 0; i < DUMP_NAME_LEN; i++)
+		efi_name[i] = stub_name[i];
+
+	/*
+	 * Clean up any entries with the same name
+	 */
+
+	list_for_each_entry(entry, &efivars->list, list) {
+		get_var_data_locked(efivars, &entry->var);
+
+		if (efi_guidcmp(entry->var.VendorGuid, vendor))
+			continue;
+		if (utf16_strncmp(entry->var.VariableName, efi_name,
+				  utf16_strlen(efi_name)))
+			continue;
+		/* Needs to be a prefix */
+		if (entry->var.VariableName[utf16_strlen(efi_name)] == 0)
+			continue;
+
+		/* found */
+		found = entry;
+		efivars->ops->set_variable(entry->var.VariableName,
+					   &entry->var.VendorGuid,
+					   PSTORE_EFI_ATTRIBUTES,
+					   0, NULL);
+	}
+
+	if (found)
+		list_del(&found->list);
+
+	spin_unlock_irqrestore(&efivars->lock, flags);
+
+	if (found)
+		efivar_unregister(found);
 
 	return 0;
 }
-- 1.7.1