Re: [PATCH] blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx

[Ming Lei]

On Tue, Aug 26, 2025 at 04:48:54PM +0800, linan666@xxxxxxxxxxxxxxx wrote:
> From: Li Nan <linan122@xxxxxxxxxx>
> 
> In __blk_mq_update_nr_hw_queues() the return value of
> blk_mq_sysfs_register_hctxs() is not checked. If sysfs creation for hctx

Looks we should check its return value and handle the failure in both
the call site and blk_mq_sysfs_register_hctxs().

> fails, later changing the number of hw_queues or removing disk will
> trigger the following warning:
> 
>   kernfs: can not remove 'nr_tags', no directory
>   WARNING: CPU: 2 PID: 637 at fs/kernfs/dir.c:1707 kernfs_remove_by_name_ns+0x13f/0x160
>   Call Trace:
>    remove_files.isra.1+0x38/0xb0
>    sysfs_remove_group+0x4d/0x100
>    sysfs_remove_groups+0x31/0x60
>    __kobject_del+0x23/0xf0
>    kobject_del+0x17/0x40
>    blk_mq_unregister_hctx+0x5d/0x80
>    blk_mq_sysfs_unregister_hctxs+0x94/0xd0
>    blk_mq_update_nr_hw_queues+0x124/0x760
>    nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
>    nullb_device_submit_queues_store+0x92/0x120 [null_blk]
> 
> kobjct_del() was called unconditionally even if sysfs creation failed.
> Fix it by checkig the kobject creation statusbefore deleting it.
> 
> Fixes: 477e19dedc9d ("blk-mq: adjust debugfs and sysfs register when updating nr_hw_queues")
> Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
> ---
>  block/blk-mq-sysfs.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 24656980f443..5c399ac562ea 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -150,9 +150,11 @@ static void blk_mq_unregister_hctx(struct blk_mq_hw_ctx *hctx)
>  		return;
>  
>  	hctx_for_each_ctx(hctx, ctx, i)
> -		kobject_del(&ctx->kobj);
> +		if (ctx->kobj.state_in_sysfs)
> +			kobject_del(&ctx->kobj);
>  
> -	kobject_del(&hctx->kobj);
> +	if (hctx->kobj.state_in_sysfs)
> +		kobject_del(&hctx->kobj);

It is bad to use kobject internal state in block layer.


Thanks,
Ming