UBI: add reboot notifier

Terminate the UBI background thread prior to restarting the system.

[Artem: amended comments a little]
Signed-off-by: NKevin Cernekee <kpc.mtd@gmail.com>
Tested-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/ubi/build.c

@@ -41,6 +41,7 @@
 #include <linux/miscdevice.h>
 #include <linux/log2.h>
 #include <linux/kthread.h>
+#include <linux/reboot.h>
 #include "ubi.h"
 
 /* Maximum length of the 'mtd=' parameter */
@@ -822,6 +823,34 @@ static int autoresize(struct ubi_device *ubi, int vol_id)
 	return 0;
 }
 
+/**
+ * ubi_reboot_notifier - halt UBI transactions immediately prior to a reboot.
+ * @n: reboot notifier object
+ * @state: SYS_RESTART, SYS_HALT, or SYS_POWER_OFF
+ * @cmd: pointer to command string for RESTART2
+ *
+ * This function stops the UBI background thread so that the flash device
+ * remains quiescent when Linux restarts the system. Any queued work will be
+ * discarded, but this function will block until do_work() finishes if an
+ * operation is already in progress.
+ *
+ * This function solves a real-life problem observed on NOR flashes when an
+ * PEB erase operation starts, then the system is rebooted before the erase is
+ * finishes, and the boot loader gets confused and dies. So we prefer to finish
+ * the ongoing operation before rebooting.
+ */
+static int ubi_reboot_notifier(struct notifier_block *n, unsigned long state,
+			       void *cmd)
+{
+	struct ubi_device *ubi;
+
+	ubi = container_of(n, struct ubi_device, reboot_notifier);
+	if (ubi->bgt_thread)
+		kthread_stop(ubi->bgt_thread);
+	ubi_sync(ubi->ubi_num);
+	return NOTIFY_DONE;
+}
+
 /**
  * ubi_attach_mtd_dev - attach an MTD device.
  * @mtd: MTD device description object
@@ -978,6 +1007,11 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
 	wake_up_process(ubi->bgt_thread);
 	spin_unlock(&ubi->wl_lock);
 
+	/* Flash device priority is 0 - UBI needs to shut down first */
+	ubi->reboot_notifier.priority = 1;
+	ubi->reboot_notifier.notifier_call = ubi_reboot_notifier;
+	register_reboot_notifier(&ubi->reboot_notifier);
+
 	ubi_devices[ubi_num] = ubi;
 	ubi_notify_all(ubi, UBI_VOLUME_ADDED, NULL);
 	return ubi_num;
@@ -1049,6 +1083,7 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
 	 * Before freeing anything, we have to stop the background thread to
 	 * prevent it from doing anything on this device while we are freeing.
 	 */
+	unregister_reboot_notifier(&ubi->reboot_notifier);
 	if (ubi->bgt_thread)
 		kthread_stop(ubi->bgt_thread);
 

drivers/mtd/ubi/ubi.h

@@ -36,9 +36,9 @@
 #include <linux/device.h>
 #include <linux/string.h>
 #include <linux/vmalloc.h>
+#include <linux/notifier.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/ubi.h>
-#include <linux/notifier.h>
 
 #include "ubi-media.h"
 #include "scan.h"
@@ -348,6 +348,7 @@ struct ubi_wl_entry;
  * @bgt_thread: background thread description object
  * @thread_enabled: if the background thread is enabled
  * @bgt_name: background thread name
+ * @reboot_notifier: notifier to terminate background thread before rebooting
  *
  * @flash_size: underlying MTD device size (in bytes)
  * @peb_count: count of physical eraseblocks on the MTD device
@@ -431,6 +432,7 @@ struct ubi_device {
 	struct task_struct *bgt_thread;
 	int thread_enabled;
 	char bgt_name[sizeof(UBI_BGT_NAME_PATTERN)+2];
+	struct notifier_block reboot_notifier;
 
 	/* I/O sub-system's stuff */
 	long long flash_size;