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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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