Re: [PATCH v2] genirq/irqdesc: fix WARNING in irq_sysfs_del()

[Yang Yingliang]

On 2022/11/29 1:20, Greg KH wrote:
> On Mon, Nov 28, 2022 at 11:16:12PM +0800, Yang Yingliang wrote:
> > I got the lots of WARNING report when doing fault injection test:
> >
> > kernfs: can not remove 'chip_name', no directory
> > WARNING: CPU: 0 PID: 253 at fs/kernfs/dir.c:1616 kernfs_remove_by_name_ns+0xce/0xe0
> > RIP: 0010:kernfs_remove_by_name_ns+0xce/0xe0
> > Call Trace:
> >   <TASK>
> >   remove_files.isra.1+0x3f/0xb0
> >   sysfs_remove_group+0x68/0xe0
> >   sysfs_remove_groups+0x41/0x70
> >   __kobject_del+0x45/0xc0
> >   kobject_del+0x29/0x40
> >   free_desc+0x42/0x70
> >   irq_free_descs+0x5e/0x90
> >
> > kernfs: can not remove 'hwirq', no directory
> > WARNING: CPU: 0 PID: 253 at fs/kernfs/dir.c:1616 kernfs_remove_by_name_ns+0xce/0xe0
> > RIP: 0010:kernfs_remove_by_name_ns+0xce/0xe0
> > Call Trace:
> >   <TASK>
> >   remove_files.isra.1+0x3f/0xb0
> >   sysfs_remove_group+0x68/0xe0
> >   sysfs_remove_groups+0x41/0x70
> >   __kobject_del+0x45/0xc0
> >   kobject_del+0x29/0x40
> >   free_desc+0x42/0x70
> >   irq_free_descs+0x5e/0x90
> >
> > If irq_sysfs_add() fails in alloc_descs(), the directory of interrupt
> > informations is not added to sysfs, it causes the WARNINGs when removing
> > the information files. Add 'sysfs_added' field in struct irq_desc to
> > indicate if it is added, and check it before calling kobject_del() to
> > avoid these WARNINGs.
> >
> > Fixes: ecb3f394c5db ("genirq: Expose interrupt information through sysfs")
> > Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> > ---
> > v1 -> v2:
> >    Don't use state_in_sysfs, introduce 'sysfs_added' to indicate if it is added.
> > ---
> >   include/linux/irqdesc.h | 1 +
> >   kernel/irq/irqdesc.c    | 7 +++++--
> >   2 files changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
> > index 844a8e30e6de..fec0f3946a34 100644
> > --- a/include/linux/irqdesc.h
> > +++ b/include/linux/irqdesc.h
> > @@ -97,6 +97,7 @@ struct irq_desc {
> >   #ifdef CONFIG_SPARSE_IRQ
> >   	struct rcu_head		rcu;
> >   	struct kobject		kobj;
> > +	bool			sysfs_added;
> >   #endif
> >   	struct mutex		request_mutex;
> >   	int			parent_irq;
> > diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> > index a91f9001103c..9bf74d11bad5 100644
> > --- a/kernel/irq/irqdesc.c
> > +++ b/kernel/irq/irqdesc.c
> > @@ -292,6 +292,8 @@ static void irq_sysfs_add(int irq, struct irq_desc *desc)
> >   		 */
> >   		if (kobject_add(&desc->kobj, irq_kobj_base, "%d", irq))
> >   			pr_warn("Failed to add kobject for irq %d\n", irq);
> > +		else
> > +			desc->sysfs_added = true;
> Wait, no.  Why are you just not properly failing and unwinding here?
We can not call kobject_put() here, it will free the 'desc' in 
irq_kobj_release(),
the irq is still in use and the 'desc' should be freed in free_desc(), 
so the failure
handled in irq_sysfs_del().

If irq_sysfs_add() fails, it does nothing except print message,
we don't know if it's added successfully while calling irq_sysfs_del(),
so I introduced a filed to store the return status that can be used in
irq_sysfs_add().

alloc_descs()
  irq_sysfs_add(desc) <-- it's failed and does nothing except print message

irq_free_descs()
  free_desc()
    irq_sysfs_del(desc) <-- it doesn't know irq_sysfs_add() is failed.
    delayed_free_desc()
      kfree(desc)

I this case, If dont' use a flag, I can not figure out a better way to
let irq_sysfs_del() know it's added failed.

Thanks,
Yang
> Why do you need a special flag just to say "sysfs worked" or not unlike
> all other users of kobjects.
>
> Fix this up properly please.
>
> thanks,
>
> greg k-h
> .