Re: 💥 PANICKED: Test report for kernel 5.9.0-rc3-020ad03.cki (block)

[Ming Lei <ming.lei@redhat.com>]

On Thu, Sep 03, 2020 at 09:37:40PM -0600, Jens Axboe wrote:
> On 9/3/20 9:22 PM, Ming Lei wrote:
> > It is one MD's bug, and percpu_ref_exit() may be called on one ref not
> > initialized via percpu_ref_init(), and the following patch can fix the
> > issue:
> 
> I really (REALLY) think this should be handled by percpu_ref_exit(), if

OK, we can do that by return immediately from percpu_ref_exit() if
percpu_count_ptr(ref) is 0 just like before.

> it worked before. Otherwise you're just setting yourself up for a world
> of pain with other users, and we'll be fixing this fallout for a while.
> I don't want to carry that. So let's just make it do the right thing,
> needing to do this:
> 
> > +       if (mddev->writes_pending.percpu_count_ptr)
> > +               percpu_ref_exit(&mddev->writes_pending);
> 
> is really nasty.

Yeah, it is as mddev_init_writes_pending():

        if (mddev->writes_pending.percpu_count_ptr)
                return 0;
        if (percpu_ref_init(&mddev->writes_pending, no_op,
                            PERCPU_REF_ALLOW_REINIT, GFP_KERNEL) < 0)
                return -ENOMEM;

thanks,
Ming