On Tue, Jul 15, 2025 at 03:43:08PM +0200, Christian König wrote:
> We are about to revert this patch. Not sure if backporting it makes sense at
> the moment.
I think it still makes sense, at least as an interim fix.
What I discussed with Thomas is that first we want to revert back from
gem_bo->dma_buf to gem_bo->import_attach.dmabuf everywhere. And those
patches are sprinkled over various branches/trees/releases. So it'll take
a while to catch them all. Meanwhile these two patches at least take care
of the worst fallout, they're already tested and in the pipeline - I don't
think it makes sense to hold them up and wait.
It might take us until 6.17-rc1 until we've caught all the trees and made
sure the backports of those reverts have happened, and I don't think we
should wait that long.
Cheers, Sima
> Regards,
> Christian.
>
> On 15.07.25 15:13, Greg Kroah-Hartman wrote:
> > 6.15-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Thomas Zimmermann <tzimmerm...@suse.de>
> >
> > commit 5307dce878d4126e1b375587318955bd019c3741 upstream.
> >
> > A GEM handle can be released while the GEM buffer object is attached
> > to a DRM framebuffer. This leads to the release of the dma-buf backing
> > the buffer object, if any. [1] Trying to use the framebuffer in further
> > mode-setting operations leads to a segmentation fault. Most easily
> > happens with driver that use shadow planes for vmap-ing the dma-buf
> > during a page flip. An example is shown below.
> >
> > [ 156.791968] ------------[ cut here ]------------
> > [ 156.796830] WARNING: CPU: 2 PID: 2255 at drivers/dma-buf/dma-buf.c:1527
> > dma_buf_vmap+0x224/0x430
> > [...]
> > [ 156.942028] RIP: 0010:dma_buf_vmap+0x224/0x430
> > [ 157.043420] Call Trace:
> > [ 157.045898] <TASK>
> > [ 157.048030] ? show_trace_log_lvl+0x1af/0x2c0
> > [ 157.052436] ? show_trace_log_lvl+0x1af/0x2c0
> > [ 157.056836] ? show_trace_log_lvl+0x1af/0x2c0
> > [ 157.061253] ? drm_gem_shmem_vmap+0x74/0x710
> > [ 157.065567] ? dma_buf_vmap+0x224/0x430
> > [ 157.069446] ? __warn.cold+0x58/0xe4
> > [ 157.073061] ? dma_buf_vmap+0x224/0x430
> > [ 157.077111] ? report_bug+0x1dd/0x390
> > [ 157.080842] ? handle_bug+0x5e/0xa0
> > [ 157.084389] ? exc_invalid_op+0x14/0x50
> > [ 157.088291] ? asm_exc_invalid_op+0x16/0x20
> > [ 157.092548] ? dma_buf_vmap+0x224/0x430
> > [ 157.096663] ? dma_resv_get_singleton+0x6d/0x230
> > [ 157.101341] ? __pfx_dma_buf_vmap+0x10/0x10
> > [ 157.105588] ? __pfx_dma_resv_get_singleton+0x10/0x10
> > [ 157.110697] drm_gem_shmem_vmap+0x74/0x710
> > [ 157.114866] drm_gem_vmap+0xa9/0x1b0
> > [ 157.118763] drm_gem_vmap_unlocked+0x46/0xa0
> > [ 157.123086] drm_gem_fb_vmap+0xab/0x300
> > [ 157.126979] drm_atomic_helper_prepare_planes.part.0+0x487/0xb10
> > [ 157.133032] ? lockdep_init_map_type+0x19d/0x880
> > [ 157.137701] drm_atomic_helper_commit+0x13d/0x2e0
> > [ 157.142671] ? drm_atomic_nonblocking_commit+0xa0/0x180
> > [ 157.147988] drm_mode_atomic_ioctl+0x766/0xe40
> > [...]
> > [ 157.346424] ---[ end trace 0000000000000000 ]---
> >
> > Acquiring GEM handles for the framebuffer's GEM buffer objects prevents
> > this from happening. The framebuffer's cleanup later puts the handle
> > references.
> >
> > Commit 1a148af06000 ("drm/gem-shmem: Use dma_buf from GEM object
> > instance") triggers the segmentation fault easily by using the dma-buf
> > field more widely. The underlying issue with reference counting has
> > been present before.
> >
> > v2:
> > - acquire the handle instead of the BO (Christian)
> > - fix comment style (Christian)
> > - drop the Fixes tag (Christian)
> > - rename err_ gotos
> > - add missing Link tag
> >
> > Suggested-by: Christian König <christian.koe...@amd.com>
> > Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
> > Link:
> > https://elixir.bootlin.com/linux/v6.15/source/drivers/gpu/drm/drm_gem.c#L241
> > # [1]
> > Cc: Thomas Zimmermann <tzimmerm...@suse.de>
> > Cc: Anusha Srivatsa <asriv...@redhat.com>
> > Cc: Christian König <christian.koe...@amd.com>
> > Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
> > Cc: Maxime Ripard <mrip...@kernel.org>
> > Cc: Sumit Semwal <sumit.sem...@linaro.org>
> > Cc: "Christian König" <christian.koe...@amd.com>
> > Cc: linux-me...@vger.kernel.org
> > Cc: dri-devel@lists.freedesktop.org
> > Cc: linaro-mm-...@lists.linaro.org
> > Cc: <sta...@vger.kernel.org>
> > Reviewed-by: Christian König <christian.koe...@amd.com>
> > Link: https://lore.kernel.org/r/20250630084001.293053-1-tzimmerm...@suse.de
> > Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> > ---
> > drivers/gpu/drm/drm_gem.c | 44
> > ++++++++++++++++++++++++---
> > drivers/gpu/drm/drm_gem_framebuffer_helper.c | 16 +++++----
> > drivers/gpu/drm/drm_internal.h | 2 +
> > 3 files changed, 51 insertions(+), 11 deletions(-)
> >
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -212,6 +212,35 @@ void drm_gem_private_object_fini(struct
> > }
> > EXPORT_SYMBOL(drm_gem_private_object_fini);
> >
> > +static void drm_gem_object_handle_get(struct drm_gem_object *obj)
> > +{
> > + struct drm_device *dev = obj->dev;
> > +
> > + drm_WARN_ON(dev, !mutex_is_locked(&dev->object_name_lock));
> > +
> > + if (obj->handle_count++ == 0)
> > + drm_gem_object_get(obj);
> > +}
> > +
> > +/**
> > + * drm_gem_object_handle_get_unlocked - acquire reference on user-space
> > handles
> > + * @obj: GEM object
> > + *
> > + * Acquires a reference on the GEM buffer object's handle. Required
> > + * to keep the GEM object alive. Call drm_gem_object_handle_put_unlocked()
> > + * to release the reference.
> > + */
> > +void drm_gem_object_handle_get_unlocked(struct drm_gem_object *obj)
> > +{
> > + struct drm_device *dev = obj->dev;
> > +
> > + guard(mutex)(&dev->object_name_lock);
> > +
> > + drm_WARN_ON(dev, !obj->handle_count); /* first ref taken in create-tail
> > helper */
> > + drm_gem_object_handle_get(obj);
> > +}
> > +EXPORT_SYMBOL(drm_gem_object_handle_get_unlocked);
> > +
> > /**
> > * drm_gem_object_handle_free - release resources bound to userspace
> > handles
> > * @obj: GEM object to clean up.
> > @@ -242,8 +271,14 @@ static void drm_gem_object_exported_dma_
> > }
> > }
> >
> > -static void
> > -drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj)
> > +/**
> > + * drm_gem_object_handle_put_unlocked - releases reference on user-space
> > handles
> > + * @obj: GEM object
> > + *
> > + * Releases a reference on the GEM buffer object's handle. Possibly
> > releases
> > + * the GEM buffer object and associated dma-buf objects.
> > + */
> > +void drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj)
> > {
> > struct drm_device *dev = obj->dev;
> > bool final = false;
> > @@ -268,6 +303,7 @@ drm_gem_object_handle_put_unlocked(struc
> > if (final)
> > drm_gem_object_put(obj);
> > }
> > +EXPORT_SYMBOL(drm_gem_object_handle_put_unlocked);
> >
> > /*
> > * Called at device or object close to release the file's
> > @@ -389,8 +425,8 @@ drm_gem_handle_create_tail(struct drm_fi
> > int ret;
> >
> > WARN_ON(!mutex_is_locked(&dev->object_name_lock));
> > - if (obj->handle_count++ == 0)
> > - drm_gem_object_get(obj);
> > +
> > + drm_gem_object_handle_get(obj);
> >
> > /*
> > * Get the user-visible handle using idr. Preload and perform
> > --- a/drivers/gpu/drm/drm_gem_framebuffer_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
> > @@ -99,7 +99,7 @@ void drm_gem_fb_destroy(struct drm_frame
> > unsigned int i;
> >
> > for (i = 0; i < fb->format->num_planes; i++)
> > - drm_gem_object_put(fb->obj[i]);
> > + drm_gem_object_handle_put_unlocked(fb->obj[i]);
> >
> > drm_framebuffer_cleanup(fb);
> > kfree(fb);
> > @@ -182,8 +182,10 @@ int drm_gem_fb_init_with_funcs(struct dr
> > if (!objs[i]) {
> > drm_dbg_kms(dev, "Failed to lookup GEM object\n");
> > ret = -ENOENT;
> > - goto err_gem_object_put;
> > + goto err_gem_object_handle_put_unlocked;
> > }
> > + drm_gem_object_handle_get_unlocked(objs[i]);
> > + drm_gem_object_put(objs[i]);
> >
> > min_size = (height - 1) * mode_cmd->pitches[i]
> > + drm_format_info_min_pitch(info, i, width)
> > @@ -193,22 +195,22 @@ int drm_gem_fb_init_with_funcs(struct dr
> > drm_dbg_kms(dev,
> > "GEM object size (%zu) smaller than minimum
> > size (%u) for plane %d\n",
> > objs[i]->size, min_size, i);
> > - drm_gem_object_put(objs[i]);
> > + drm_gem_object_handle_put_unlocked(objs[i]);
> > ret = -EINVAL;
> > - goto err_gem_object_put;
> > + goto err_gem_object_handle_put_unlocked;
> > }
> > }
> >
> > ret = drm_gem_fb_init(dev, fb, mode_cmd, objs, i, funcs);
> > if (ret)
> > - goto err_gem_object_put;
> > + goto err_gem_object_handle_put_unlocked;
> >
> > return 0;
> >
> > -err_gem_object_put:
> > +err_gem_object_handle_put_unlocked:
> > while (i > 0) {
> > --i;
> > - drm_gem_object_put(objs[i]);
> > + drm_gem_object_handle_put_unlocked(objs[i]);
> > }
> > return ret;
> > }
> > --- a/drivers/gpu/drm/drm_internal.h
> > +++ b/drivers/gpu/drm/drm_internal.h
> > @@ -161,6 +161,8 @@ void drm_sysfs_lease_event(struct drm_de
> >
> > /* drm_gem.c */
> > int drm_gem_init(struct drm_device *dev);
> > +void drm_gem_object_handle_get_unlocked(struct drm_gem_object *obj);
> > +void drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj);
> > int drm_gem_handle_create_tail(struct drm_file *file_priv,
> > struct drm_gem_object *obj,
> > u32 *handlep);
> >
> >
>
--
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
