netdev - Re: [PATCH V7 mlx5-next 14/15] vfio/mlx5: Use its own PCI reset

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Message-ID: <20220209023918.GO4160@nvidia.com>
Date:   Tue, 8 Feb 2022 22:39:18 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Yishai Hadas <yishaih@...dia.com>, bhelgaas@...gle.com,
        saeedm@...dia.com, linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, kuba@...nel.org, leonro@...dia.com,
        kwankhede@...dia.com, mgurtovoy@...dia.com, maorg@...dia.com,
        ashok.raj@...el.com, kevin.tian@...el.com,
        shameerali.kolothum.thodi@...wei.com
Subject: Re: [PATCH V7 mlx5-next 14/15] vfio/mlx5: Use its own PCI reset_done
 error handler

On Tue, Feb 08, 2022 at 05:08:01PM -0700, Alex Williamson wrote:
> > @@ -477,10 +499,34 @@ static int mlx5vf_pci_get_device_state(struct vfio_device *vdev,
> >  
> >  	mutex_lock(&mvdev->state_mutex);
> >  	*curr_state = mvdev->mig_state;
> > -	mutex_unlock(&mvdev->state_mutex);
> > +	mlx5vf_state_mutex_unlock(mvdev);
> >  	return 0;
> 
> I still can't see why it wouldn't be a both fairly trivial to implement
> and a usability improvement if the unlock wrapper returned -EAGAIN on a
> deferred reset so we could avoid returning a stale state to the user
> and a dead fd in the former case.  Thanks,

It simply is not useful - again, we always resolve this race that
should never happen as though the two events happened consecutively,
which is what would normally happen if we could use a simple mutex. We
do not need to add any more complexity to deal with this already
troublesome thing..

Jason