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

[Yu Kuai]

Hi,

在 2025/08/27 8:58, Ming Lei 写道:
> 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().

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@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
>
>
> .