Re: [PATCH] block: fix deadlock between bd_link_disk_holder and partition scan

[Song Liu]

On Wed, Feb 7, 2024 at 1:32 AM <linan666@xxxxxxxxxxxxxxx> wrote:
>
> From: Li Nan <linan122@xxxxxxxxxx>
>
> 'open_mutex' of gendisk is used to protect open/close block devices. But
> in bd_link_disk_holder(), it is used to protect the creation of symlink
> between holding disk and slave bdev, which introduces some issues.
>
> When bd_link_disk_holder() is called, the driver is usually in the process
> of initialization/modification and may suspend submitting io. At this
> time, any io hold 'open_mutex', such as scanning partitions, can cause
> deadlocks. For example, in raid:
>
> T1                              T2
> bdev_open_by_dev
>  lock open_mutex [1]
>  ...
>   efi_partition
>   ...
>    md_submit_bio
>                                 md_ioctl mddev_syspend
>                                   -> suspend all io
>                                  md_add_new_disk
>                                   bind_rdev_to_array
>                                    bd_link_disk_holder
>                                     try lock open_mutex [2]
>     md_handle_request
>      -> wait mddev_resume
>
> T1 scan partition, T2 add a new device to raid. T1 waits for T2 to resume
> mddev, but T2 waits for open_mutex held by T1. Deadlock occurs.
>
> Fix it by introducing a local mutex 'holder_mutex' to replace 'open_mutex'.

Is this to fix [1]? Do we need some Fixes and/or Closes tags?

Could you please add steps to reproduce this issue?

Thanks,
Song

[1] https://bugzilla.kernel.org/show_bug.cgi?id=218459

>
> Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
> ---
>  block/holder.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/block/holder.c b/block/holder.c
> index 37d18c13d958..5bfb0a674cc7 100644
> --- a/block/holder.c
> +++ b/block/holder.c
> @@ -8,6 +8,8 @@ struct bd_holder_disk {
>         int                     refcnt;
>  };
>
> +static DEFINE_MUTEX(holder_mutex);
> +
>  static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
>                                                   struct gendisk *disk)
>  {
> @@ -80,7 +82,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
>         kobject_get(bdev->bd_holder_dir);
>         mutex_unlock(&bdev->bd_disk->open_mutex);
>
> -       mutex_lock(&disk->open_mutex);
> +       mutex_lock(&holder_mutex);
>         WARN_ON_ONCE(!bdev->bd_holder);
>
>         holder = bd_find_holder_disk(bdev, disk);
> @@ -108,7 +110,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
>                 goto out_del_symlink;
>         list_add(&holder->list, &disk->slave_bdevs);
>
> -       mutex_unlock(&disk->open_mutex);
> +       mutex_unlock(&holder_mutex);
>         return 0;
>
>  out_del_symlink:
> @@ -116,7 +118,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
>  out_free_holder:
>         kfree(holder);
>  out_unlock:
> -       mutex_unlock(&disk->open_mutex);
> +       mutex_unlock(&holder_mutex);
>         if (ret)
>                 kobject_put(bdev->bd_holder_dir);
>         return ret;
> @@ -140,7 +142,7 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
>         if (WARN_ON_ONCE(!disk->slave_dir))
>                 return;
>
> -       mutex_lock(&disk->open_mutex);
> +       mutex_lock(&holder_mutex);
>         holder = bd_find_holder_disk(bdev, disk);
>         if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
>                 del_symlink(disk->slave_dir, bdev_kobj(bdev));
> @@ -149,6 +151,6 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
>                 list_del_init(&holder->list);
>                 kfree(holder);
>         }
> -       mutex_unlock(&disk->open_mutex);
> +       mutex_unlock(&holder_mutex);
>  }
>  EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
> --
> 2.39.2
>