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    SubjectRe: [PATCH] block: prevent sending events from removed device
    On Wed, Jun 30, 2021 at 08:09:39AM +0000, Christian L?hle wrote:
    > Skip kobject_uevent_env in case the associated kobject
    > no longer exists, as calling kobject_uevent_env with
    > NULL is not safe.
    >

    I don't see how this is going to work. If the device is being
    deleted the reference count will be zero and refcount_inc as
    called from kobject_get will WARN. We'll need to check the
    disk is marked up, and we need to do that under a lock.

    Something like this completely untested patch:

    diff --git a/block/disk-events.c b/block/disk-events.c
    index a75931ff5da4..27b845c51f2a 100644
    --- a/block/disk-events.c
    +++ b/block/disk-events.c
    @@ -190,6 +190,9 @@ static void disk_check_events(struct disk_events *ev,

    spin_unlock_irq(&ev->lock);

    + if (!(disk->flags & GENHD_FL_UP))
    + return;
    +
    /*
    * Tell userland about new events. Only the events listed in
    * @disk->events are reported, and only if DISK_EVENT_FLAG_UEVENT
    @@ -268,6 +271,8 @@ bool bdev_check_media_change(struct block_device *bdev)
    {
    unsigned int events;

    + lockdep_assert_held(&bdev->bd_disk->open_mutex);
    +
    events = disk_clear_events(bdev->bd_disk, DISK_EVENT_MEDIA_CHANGE |
    DISK_EVENT_EJECT_REQUEST);
    if (!(events & DISK_EVENT_MEDIA_CHANGE))
    @@ -290,7 +295,10 @@ static void disk_events_workfn(struct work_struct *work)
    struct delayed_work *dwork = to_delayed_work(work);
    struct disk_events *ev = container_of(dwork, struct disk_events, dwork);

    - disk_check_events(ev, &ev->clearing);
    + mutex_lock(&ev->disk->open_mutex);
    + if (ev->disk->flags & GENHD_FL_UP)
    + disk_check_events(ev, &ev->clearing);
    + mutex_unlock(&ev->disk->open_mutex);
    }

    /*
    diff --git a/drivers/block/ataflop.c b/drivers/block/ataflop.c
    index a093644ac39f..b8e77da44235 100644
    --- a/drivers/block/ataflop.c
    +++ b/drivers/block/ataflop.c
    @@ -1735,8 +1735,10 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode,
    /* invalidate the buffer track to force a reread */
    BufferDrive = -1;
    set_bit(drive, &fake_change);
    + mutex_lock(&bdev->bd_disk->open_mutex);
    if (bdev_check_media_change(bdev))
    floppy_revalidate(bdev->bd_disk);
    + mutex_unlock(&bdev->bd_disk->open_mutex);
    return 0;
    default:
    return -EINVAL;
    diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
    index 87460e0e5c72..2a97f22cfa0b 100644
    --- a/drivers/block/floppy.c
    +++ b/drivers/block/floppy.c
    @@ -3185,8 +3185,10 @@ static int invalidate_drive(struct block_device *bdev)
    /* invalidate the buffer track to force a reread */
    set_bit((long)bdev->bd_disk->private_data, &fake_change);
    process_fd_request();
    + mutex_lock(&bdev->bd_disk->open_mutex);
    if (bdev_check_media_change(bdev))
    floppy_revalidate(bdev->bd_disk);
    + mutex_unlock(&bdev->bd_disk->open_mutex);
    return 0;
    }

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