Re: [PATCH v4 07/11] liveupdate: Auto unregister FLBs on file handler unregistration

[Mike Rapoport <rppt@kernel.org>]

On Mon, Apr 13, 2026 at 06:51:23PM +0000, Pasha Tatashin wrote:
> To ensure that unregistration is always successful and doesn't leave
> dangling resources, introduce auto-unregistration of FLBs: when a file
> handler is unregistered, all FLBs associated with it are automatically
> unregistered.
> 
> Introduce a new helper luo_flb_unregister_all() which unregisters all
> FLBs linked to the given file handler.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  kernel/liveupdate/luo_file.c     | 14 +-----
>  kernel/liveupdate/luo_flb.c      | 85 ++++++++++++++++++++++----------
>  kernel/liveupdate/luo_internal.h |  1 +
>  3 files changed, 61 insertions(+), 39 deletions(-)
> 
> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> index 63ddcf6dcddb..b37bd79974ce 100644
> --- a/kernel/liveupdate/luo_file.c
> +++ b/kernel/liveupdate/luo_file.c
> @@ -926,26 +926,16 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
>   */
>  int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
>  {
> -	int err = -EBUSY;
> -
>  	if (!liveupdate_enabled())
>  		return -EOPNOTSUPP;
>  
>  	liveupdate_test_unregister(fh);
>  
> -	down_write(&luo_register_rwlock);
> -	if (!list_empty(&ACCESS_PRIVATE(fh, flb_list)))
> -		goto err_unlock;
> -
> +	guard(rwsem_write)(&luo_register_rwlock);
> +	luo_flb_unregister_all(fh);
>  	list_del(&ACCESS_PRIVATE(fh, list));
> -	up_write(&luo_register_rwlock);
>  
>  	module_put(fh->ops->owner);
>  
>  	return 0;
> -
> -err_unlock:
> -	up_write(&luo_register_rwlock);
> -	liveupdate_test_register(fh);
> -	return err;
>  }
> diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
> index 13f96d11ecc9..b9f5d452a998 100644
> --- a/kernel/liveupdate/luo_flb.c
> +++ b/kernel/liveupdate/luo_flb.c
> @@ -318,6 +318,63 @@ void luo_flb_file_finish(struct liveupdate_file_handler *fh)
>  		luo_flb_file_finish_one(iter->flb);
>  }
>  
> +static void luo_flb_unregister_one(struct liveupdate_file_handler *fh,
> +				   struct liveupdate_flb *flb)
> +{
> +	struct luo_flb_private *private = luo_flb_get_private(flb);
> +	struct list_head *flb_list = &ACCESS_PRIVATE(fh, flb_list);
> +	struct luo_flb_link *iter;
> +	bool found = false;
> +
> +	/* Find and remove the link from the file handler's list */
> +	lockdep_assert_held_write(&luo_register_rwlock);
> +	list_for_each_entry(iter, flb_list, list) {
> +		if (iter->flb == flb) {
> +			list_del(&iter->list);
> +			kfree(iter);
> +			found = true;
> +			break;
> +		}
> +	}
> +
> +	if (!found) {
> +		pr_warn("Failed to unregister FLB '%s': not found in file handler '%s'\n",
> +			flb->compatible, fh->compatible);
> +		return;
> +	}
> +
> +	private->users--;
> +
> +	/*
> +	 * If this is the last file-handler with which we are registred, remove
> +	 * from the global list.
> +	 */
> +	if (!private->users) {
> +		list_del_init(&private->list);
> +		luo_flb_global.count--;
> +	}
> +}
> +
> +/**
> + * luo_flb_unregister_all - Unregister all FLBs associated with a file handler.
> + * @fh: The file handler whose FLBs should be unregistered.
> + *
> + * This function iterates through the list of FLBs associated with the given
> + * file handler and unregisters them all one by one.
> + */
> +void luo_flb_unregister_all(struct liveupdate_file_handler *fh)
> +{
> +	struct list_head *flb_list = &ACCESS_PRIVATE(fh, flb_list);
> +	struct luo_flb_link *iter, *tmp;
> +
> +	if (!liveupdate_enabled())
> +		return;
> +
> +	lockdep_assert_held_write(&luo_register_rwlock);
> +	list_for_each_entry_safe(iter, tmp, flb_list, list)
> +		luo_flb_unregister_one(fh, iter->flb);
> +}
> +
>  /**
>   * liveupdate_register_flb - Associate an FLB with a file handler and register it globally.
>   * @fh:   The file handler that will now depend on the FLB.
> @@ -426,38 +483,12 @@ int liveupdate_register_flb(struct liveupdate_file_handler *fh,
>  int liveupdate_unregister_flb(struct liveupdate_file_handler *fh,
>  			      struct liveupdate_flb *flb)
>  {
> -	struct luo_flb_private *private = luo_flb_get_private(flb);
> -	struct list_head *flb_list = &ACCESS_PRIVATE(fh, flb_list);
> -	struct luo_flb_link *iter;
> -	int err = -ENOENT;
> -
>  	if (!liveupdate_enabled())
>  		return -EOPNOTSUPP;
>  
>  	guard(rwsem_write)(&luo_register_rwlock);
>  
> -	/* Find and remove the link from the file handler's list */
> -	list_for_each_entry(iter, flb_list, list) {
> -		if (iter->flb == flb) {
> -			list_del(&iter->list);
> -			kfree(iter);
> -			err = 0;
> -			break;
> -		}
> -	}
> -
> -	if (err)
> -		return err;
> -
> -	private->users--;
> -	/*
> -	 * If this is the last file-handler with which we are registred, remove
> -	 * from the global list.
> -	 */
> -	if (!private->users) {
> -		list_del_init(&private->list);
> -		luo_flb_global.count--;
> -	}
> +	luo_flb_unregister_one(fh, flb);
>  
>  	return 0;
>  }
> diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
> index 40a011bdfa55..22f6901f89ed 100644
> --- a/kernel/liveupdate/luo_internal.h
> +++ b/kernel/liveupdate/luo_internal.h
> @@ -103,6 +103,7 @@ void luo_file_set_destroy(struct luo_file_set *file_set);
>  int luo_flb_file_preserve(struct liveupdate_file_handler *fh);
>  void luo_flb_file_unpreserve(struct liveupdate_file_handler *fh);
>  void luo_flb_file_finish(struct liveupdate_file_handler *fh);
> +void luo_flb_unregister_all(struct liveupdate_file_handler *fh);
>  int __init luo_flb_setup_outgoing(void *fdt);
>  int __init luo_flb_setup_incoming(void *fdt);
>  void luo_flb_serialize(void);
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.