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

[Yu Kuai <yukuai1@huaweicloud.com>]

Hi,

在 2025/08/27 8:58, Ming Lei 写道:
> On Tue, Aug 26, 2025 at 04:48:54PM +0800, linan666@huaweicloud.com wrote:
>> From: Li Nan <linan122@huawei.com>
>>
>> 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().

 From __blk_mq_update_nr_hw_queues(), the old hctxs is already
unregistered, and this function is void, we failed to register new hctxs
because of memory allocation failure. I really don't know how to handle
the failure here, do you have any suggestions?

Thanks,
Kuai

> 
>> 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@huawei.com>
>> ---
>>   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
> 
> 
> .
>