linux-kernel - Re: [PATCH v3 03/11] iommufd: Introduce IOMMUFD_OBJ

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Message-ID: <CABQgh9Ft=xxJK-bjS6wCZ5BN4AiKtF9fzdBkevA3x2yb_4O4Kg@mail.gmail.com>
Date: Sat, 12 Oct 2024 18:18:01 +0800
From: Zhangfei Gao <zhangfei.gao@...aro.org>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, will@...nel.org, joro@...tes.org, 
	suravee.suthikulpanit@....com, robin.murphy@....com, dwmw2@...radead.org, 
	baolu.lu@...ux.intel.com, shuah@...nel.org, linux-kernel@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com, 
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com, 
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com, yi.l.liu@...el.com, 
	aik@....com, patches@...ts.linux.dev
Subject: Re: [PATCH v3 03/11] iommufd: Introduce IOMMUFD_OBJ_VIOMMU and its
 related struct

On Sat, 12 Oct 2024 at 12:49, Nicolin Chen <nicolinc@...dia.com> wrote:
>
> On Sat, Oct 12, 2024 at 11:23:07AM +0800, Zhangfei Gao wrote:
>
> > > diff --git a/drivers/iommu/iommufd/viommu_api.c b/drivers/iommu/iommufd/viommu_api.c
> > > new file mode 100644
> > > index 000000000000..c1731f080d6b
> > > --- /dev/null
> > > +++ b/drivers/iommu/iommufd/viommu_api.c
> > > @@ -0,0 +1,57 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/* Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES
> > > + */
> > > +
> > > +#include "iommufd_private.h"
> > > +
> > > +struct iommufd_object *iommufd_object_alloc_elm(struct iommufd_ctx *ictx,
> > > +                                               size_t size,
> > > +                                               enum iommufd_object_type type)
> > > +{
> > > +       struct iommufd_object *obj;
> > > +       int rc;
> > > +
> > > +       obj = kzalloc(size, GFP_KERNEL_ACCOUNT);
> > > +       if (!obj)
> > > +               return ERR_PTR(-ENOMEM);
> > > +       obj->type = type;
> > > +       /* Starts out bias'd by 1 until it is removed from the xarray */
> > > +       refcount_set(&obj->shortterm_users, 1);
> > > +       refcount_set(&obj->users, 1);
> >
> > here set refcont 1
> >
> > iommufd_device_bind -> iommufd_object_alloc(ictx, idev,
> > IOMMUFD_OBJ_DEVICE): refcont -> 1
> > refcount_inc(&idev->obj.users); refcount -> 2
> > will cause iommufd_device_unbind fail.
> >
> > May remove refcount_inc(&idev->obj.users) in iommufd_device_bind
>
> Hmm, why would it fail? Or is it failing on your system?

Not sure, still in check, it may only be on my platform.

it hit
iommufd_object_remove:
if (WARN_ON(obj != to_destroy))

iommufd_device_bind refcount=2
iommufd_device_attach refcount=3
//still not sure which operation inc the count?
iommufd_device_detach refcount=4

Thanks



>
> This patch doesn't change the function but only moved it..
>
> Thanks
> Nicolin