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Subject[PATCH] MTD: Add UBI reboot notifier
ubifs_sync_fs() may queue up a new UBI erase transaction, which is
processed in the background:

bash# sync
ubifs_sync_fs: enter
schedule_erase: enter
schedule_erase: exit
ubi_sync: enter
ubi_sync: exit
ubifs_sync_fs: exit
cfi_amdstd_erase_varsize: enter
bash# cfi_amdstd_erase_varsize: exit

Normally this is not a big deal. However, during the final sync before
rebooting, it initiates an erase operation that is potentially still
active when Linux restarts the machine:

bash# reboot -f
ubifs_sync_fs: enter
schedule_erase: enter
schedule_erase: exit
ubi_sync: enter
ubi_sync: exit
ubifs_sync_fs: exit
cfi_amdstd_erase_varsize: enter
Restarting system.
<Flash is stuck in FL_ERASE mode - system hangs>

This is easiest to observe on a NOR flash. One factor is the long erase
time. The other reason is because getting a NOR flash stuck in FL_ERASE
mode will prevent the bootloader from running, unless the board provides
a way for the processor to automatically reset the flash. In my
experience, many boards do not.

My proposal is to add a reboot notifier to let the UBI background thread
terminate gracefully. The new ordering looks like this:

bash# reboot -f
ubifs_sync_fs: enter
schedule_erase: enter
schedule_erase: exit
ubifs_sync_fs: exit
cfi_amdstd_erase_varsize: enter
ubi_reboot_notifier: enter
cfi_amdstd_erase_varsize: exit
ubi_reboot_notifier: exit
cfi_amdstd_reboot: enter
cfi_amdstd_reboot: exit

cfi_amdstd_reboot doesn't really exist, but I added a dummy notifier to
make sure that the ordering would be correct when using drivers that do
have this feature.

Signed-off-by: Kevin Cernekee <kpc.mtd@gmail.com>
---
drivers/mtd/ubi/build.c | 24 ++++++++++++++++++++++++
drivers/mtd/ubi/ubi.h | 2 ++
2 files changed, 26 insertions(+), 0 deletions(-)
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 4048db8..ca88059 100644
--- a/drivers/mtd/ubi/build.c
+++ b/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 */
@@ -726,6 +727,23 @@ static int autoresize(struct ubi_device *ubi, int vol_id)
}

/**
+ * ubi_reboot_notifier - halt UBI transactions immediately prior to a reboot
+ * @n: notifier_block struct (inside our struct ubi_device)
+ * @val: unused
+ * @v: unused
+ */
+static int ubi_reboot_notifier(struct notifier_block *n, unsigned long val,
+ void *v)
+{
+ struct ubi_device *ubi = container_of(n, struct ubi_device,
+ reboot_notifier);
+
+ if (ubi->bgt_thread)
+ kthread_stop(ubi->bgt_thread);
+ return NOTIFY_DONE;
+}
+
+/**
* ubi_attach_mtd_dev - attach an MTD device.
* @mtd: MTD device description object
* @ubi_num: number to assign to the new UBI device
@@ -876,6 +894,11 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
ubi->thread_enabled = 1;
wake_up_process(ubi->bgt_thread);

+ /* 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;
return ubi_num;

@@ -945,6 +968,7 @@ 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);

diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index c055511..44a45b9 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -36,6 +36,7 @@
#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>

@@ -420,6 +421,7 @@ 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;
--
1.6.3.1


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