Re: [PATCH 07/23] md/md-bitmap: delay registration of bitmap_ops until creating bitmap

[Hannes Reinecke]

On 5/27/25 09:53, Yu Kuai wrote:
> Hi,
>
> 在 2025/05/27 14:13, Hannes Reinecke 写道:
> > On 5/24/25 08:13, Yu Kuai wrote:
> > > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> > >
> > > Currently bitmap_ops is registered while allocating mddev, this is fine
> > > when there is only one bitmap_ops, however, after introduing a new
> > > bitmap_ops, user space need a time window to choose which bitmap_ops to
> > > use while creating new array.
[ .. ]
> > > @@ -6093,11 +6104,6 @@ struct mddev *md_alloc(dev_t dev, char *name)
> > >           return ERR_PTR(error);
> > >       }
> > > -    if (md_bitmap_registered(mddev) && mddev->bitmap_ops->group)
> > > -        if (sysfs_create_group(&mddev->kobj, mddev->bitmap_ops->group))
> > > -            pr_warn("md: cannot register extra bitmap attributes for 
> > > %s\n",
> > > -                mdname(mddev));
> > > -
> > >       kobject_uevent(&mddev->kobj, KOBJ_ADD);
> > >       mddev->sysfs_state = sysfs_get_dirent_safe(mddev->kobj.sd, 
> > > "array_state");
> > >       mddev->sysfs_level = sysfs_get_dirent_safe(mddev->kobj.sd, 
> > > "level");
> >
> > But now you've killed udev event processing.
> > Once the 'add' event is sent _all_ sysfs attributes must be present,
> > otherwise you'll have a race condition where udev is checking for
> > attributes which are present only later.
> >
> > So when moving things around ensure to move the kobject_uevent() call, 
> > too.
>
> I do not expect the bitmap entries are checked by udev, otherwise this
> set can introduce regressions since the bitmap entries are no longer
> existed after using the new biltmap.
>
> And the above KOBJ_ADD uevent is used for mddev->kobj, right? In this
> case, we're creating new entries under mddev->kobj, should this be
> KOBJ_CHANGE?
Yes, please.

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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