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Message-ID: <aFkZaoPXkZWaqWID@e110455-lin.cambridge.arm.com>
Date: Mon, 23 Jun 2025 10:07:54 +0100
From: Liviu Dudau <liviu.dudau@....com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Chia-I Wu <olvaffe@...il.com>, Steven Price <steven.price@....com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] panthor: save panthor_file in panthor_group
On Mon, Jun 23, 2025 at 08:21:22AM +0200, Boris Brezillon wrote:
> On Fri, 20 Jun 2025 16:50:51 -0700
> Chia-I Wu <olvaffe@...il.com> wrote:
>
> > We would like to access panthor_file from panthor_group on gpu errors.
> > Because panthour_group can outlive drm_file, add refcount to
> > panthor_file to ensure its lifetime.
>
> I'm not a huge fan of refcounting panthor_file because people tend to
> put resource they expect to be released when the last handle goes away,
> and if we don't refcount these sub-resources they might live longer
> than they are meant to. Also not a huge fan of the circular referencing
> that exists between file and groups after this change.
>
> How about we move the process info to a sub-object that's refcounted
> and let both panthor_file and panthor_group take a ref on this object
> instead?
I agree with Boris on this. One alternative is to put the pid and comm in
the panthor_group struct as panthor_file makes no use of the fields.
Best regards,
Liviu
>
> >
> > Signed-off-by: Chia-I Wu <olvaffe@...il.com>
> > ---
> > drivers/gpu/drm/panthor/panthor_device.h | 16 ++++++++++++++++
> > drivers/gpu/drm/panthor/panthor_drv.c | 15 ++++++++++++++-
> > drivers/gpu/drm/panthor/panthor_mmu.c | 1 +
> > drivers/gpu/drm/panthor/panthor_sched.c | 6 ++++++
> > 4 files changed, 37 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> > index 4fc7cf2aeed57..75ae6fd3a5128 100644
> > --- a/drivers/gpu/drm/panthor/panthor_device.h
> > +++ b/drivers/gpu/drm/panthor/panthor_device.h
> > @@ -256,8 +256,24 @@ struct panthor_file {
> >
> > /** @stats: cycle and timestamp measures for job execution. */
> > struct panthor_gpu_usage stats;
> > +
> > + /** @refcount: ref count of this file */
> > + struct kref refcount;
> > };
> >
> > +static inline struct panthor_file *panthor_file_get(struct panthor_file *pfile)
> > +{
> > + kref_get(&pfile->refcount);
> > + return pfile;
> > +}
> > +
> > +void panthor_file_release(struct kref *kref);
> > +
> > +static inline void panthor_file_put(struct panthor_file *pfile)
> > +{
> > + kref_put(&pfile->refcount, panthor_file_release);
> > +}
> > +
> > int panthor_device_init(struct panthor_device *ptdev);
> > void panthor_device_unplug(struct panthor_device *ptdev);
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> > index 775a66c394544..aea9609684b77 100644
> > --- a/drivers/gpu/drm/panthor/panthor_drv.c
> > +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> > @@ -1393,6 +1393,16 @@ static int panthor_ioctl_set_user_mmio_offset(struct drm_device *ddev,
> > return 0;
> > }
> >
> > +void panthor_file_release(struct kref *kref)
> > +{
> > + struct panthor_file *pfile =
> > + container_of(kref, struct panthor_file, refcount);
> > +
> > + WARN_ON(pfile->vms || pfile->groups);
> > +
> > + kfree(pfile);
> > +}
> > +
> > static int
> > panthor_open(struct drm_device *ddev, struct drm_file *file)
> > {
> > @@ -1426,6 +1436,8 @@ panthor_open(struct drm_device *ddev, struct drm_file *file)
> > if (ret)
> > goto err_destroy_vm_pool;
> >
> > + kref_init(&pfile->refcount);
> > +
> > file->driver_priv = pfile;
> > return 0;
> >
> > @@ -1442,10 +1454,11 @@ panthor_postclose(struct drm_device *ddev, struct drm_file *file)
> > {
> > struct panthor_file *pfile = file->driver_priv;
> >
> > + /* destroy vm and group handles now to avoid circular references */
> > panthor_group_pool_destroy(pfile);
> > panthor_vm_pool_destroy(pfile);
> >
> > - kfree(pfile);
> > + panthor_file_put(pfile);
> > }
> >
> > static const struct drm_ioctl_desc panthor_drm_driver_ioctls[] = {
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > index b39ea6acc6a96..ccbcfe11420ac 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -1604,6 +1604,7 @@ void panthor_vm_pool_destroy(struct panthor_file *pfile)
> >
> > xa_destroy(&pfile->vms->xa);
> > kfree(pfile->vms);
> > + pfile->vms = NULL;
> > }
> >
> > /**
> > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> > index a2248f692a030..485072904cd7d 100644
> > --- a/drivers/gpu/drm/panthor/panthor_sched.c
> > +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> > @@ -535,6 +535,9 @@ struct panthor_group {
> > /** @ptdev: Device. */
> > struct panthor_device *ptdev;
> >
> > + /** @pfile: File this group is created from. */
> > + struct panthor_file *pfile;
> > +
> > /** @vm: VM bound to the group. */
> > struct panthor_vm *vm;
> >
> > @@ -919,6 +922,7 @@ static void group_release_work(struct work_struct *work)
> > panthor_kernel_bo_destroy(group->syncobjs);
> >
> > panthor_vm_put(group->vm);
> > + panthor_file_put(group->pfile);
> > kfree(group);
> > }
> >
> > @@ -3467,6 +3471,8 @@ int panthor_group_create(struct panthor_file *pfile,
> > INIT_WORK(&group->tiler_oom_work, group_tiler_oom_work);
> > INIT_WORK(&group->release_work, group_release_work);
> >
> > + group->pfile = panthor_file_get(pfile);
> > +
> > group->vm = panthor_vm_pool_get_vm(pfile->vms, group_args->vm_id);
> > if (!group->vm) {
> > ret = -EINVAL;
>
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
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