linux-kernel - Re: WARNING in ib_umad_kill

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Date:   Tue, 7 Apr 2020 08:55:48 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        syzbot <syzbot+9627a92b1f9262d5d30c@...kaller.appspotmail.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Rafael Wysocki <rafael@...nel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING in ib_umad_kill_port

On Tue, Apr 07, 2020 at 11:56:30AM +0200, Dmitry Vyukov wrote:
> > I'm not sure what could be done wrong here to elicit this:
> >
> >  sysfs group 'power' not found for kobject 'umad1'
> >
> > ??
> >
> > I've seen another similar sysfs related trigger that we couldn't
> > figure out.
> >
> > Hard to investigate without a reproducer.
> 
> Based on all of the sysfs-related bugs I've seen, my bet would be on
> some races. E.g. one thread registers devices, while another
> unregisters these.

I did check that the naming is ordered right, at least we won't be
concurrently creating and destroying umadX sysfs of the same names.

I'm also fairly sure we can't be destroying the parent at the same
time as this child.

Do you see the above commonly? Could it be some driver core thing? Or
is it more likely something wrong in umad?

Jason