Re: [PATCH v2] drm/gem: Fix GEM handle release errors
From: Chen Jeffy
Date: Tue Aug 09 2022 - 04:54:43 EST
Hi Christian,
On 8/9 星期二 15:55, Christian König wrote:
Am 09.08.22 um 03:28 schrieb Chen Jeffy:
Hi Christian,
On 8/9 星期二 2:03, Christian König wrote:
Hi Jeffy,
Am 08.08.22 um 05:51 schrieb Chen Jeffy:
Hi Christian,
Thanks for your reply, and sorry i didn't make it clear.
On 8/8 星期一 0:52, Christian König wrote:
Am 03.08.22 um 10:32 schrieb Jeffy Chen:
Currently we are assuming a one to one mapping between dmabuf and
handle
when releasing GEM handles.
But that is not always true, since we would create extra handles
for the
GEM obj in cases like gem_open() and getfb{,2}().
A similar issue was reported at:
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20211105083308.392156-1-jay.xu%40rock-chips.com%2F&data=05%7C01%7Cchristian.koenig%40amd.com%7C52cd6ca16a3a415b92a708da79a67dec%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637956053232922419%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=hIuH18B10sbVAyS0D4iK6R6WYc%2BZ7mlxGcKdUae%2BW6Y%3D&reserved=0
Another problem is that the drm_gem_remove_prime_handles() now only
remove handle to the exported dmabuf (gem_obj->dma_buf), so the
imported
ones would leak:
WARNING: CPU: 2 PID: 236 at drivers/gpu/drm/drm_prime.c:228
drm_prime_destroy_file_private+0x18/0x24
Let's fix these by using handle to find the exact map to remove.
Well we are clearly something missing here. As far as I can see the
current code is correct.
Creating multiple GEM handles for the same DMA-buf is possible, but
illegal. >
In other words when a GEM handle is exported as DMA-buf and
imported again you should intentionally always get the same handle.
These issue are not about having handles for importing an exported
dma-buf case, but for having multiple handles to a GEM object(which
means having multiple handles to a dma-buf).
I know the drm-prime is trying to make dma-buf and handle maps one
to one, but the drm-gem is allowing to create extra handles for a
GEM object, for example:
drm_gem_open_ioctl -> drm_gem_handle_create_tail
drm_mode_getfb2_ioctl -> drm_gem_handle_create
drm_mode_getfb -> fb->funcs->create_handle
Yes, so far that's correct.
So we are allowing GEM object to have multiple handles, and GEM
object could have at most one dma-buf, doesn't that means that
dma-buf could map to multiple handles?
No, at least not for the same GEM file private. That's the reason why
the rb is indexed by the dma_buf object and not the handle.
In other words the rb is so that you have exactly one handle for each
dma_buf in each file private.
I don't think so, because if user get multiple handles for the same
GEM obj and use drm_gem_prime_handle_to_fd() for those handles
Mhm, that works? This is illegal and should have been prevented somehow.
Let me double check the code.
Thanks for pointing that out,
Christian.
Thanks for checking it, my test case is a preload library which hooks
the drmModeSetCrtc(and other APIs) then use drmModeGetFB to extract
dmafd from fb_id.
, the current code would try to add multiple maps to rb:
drm_prime_add_buf_handle(buf_1, hdl_1)
drm_prime_add_buf_handle(buf_1, hdl_2)
...
drm_prime_add_buf_handle(buf_1, hdl_n)
Or should we rewrite the GEM framework to limit GEM object with uniq
handle?
No, the extra handles are expected because when you call
drm_mode_getfb*() and drm_gem_open_ioctl() the caller now owns the
returned GEM handle.
The other issue is that we are leaking dma-buf <-> handle map for
the imported dma-buf, since the drm_gem_remove_prime_handles doesn't
take care of obj->import_attach->dmabuf.
No, that's correct as well. obj->dma_buf is set even for imported
DMA-buf objects. See drm_gem_prime_fd_to_handle().
Well, that obj->dma_buf would be set in
drm_gem_prime_fd_to_handle(create new handle), and cleared when
releasing the latest handle(release handle).
So it doesn't cover other handle creating path.
For example, a imported dma buf:
drm_gem_prime_fd_to_handle <-- we got a handle and obj->dma_buf and
obj->import_attach->dmabuf
drm_gem_handle_delete <-- we lost that handle and obj->dma_buf cleared
drm_gem_open_ioctl/or getfb* <-- we got a new handle and
obj->import_attach->dmabuf
drm_gem_handle_delete <-- we lost that handle and obj->dma_buf is
null, which means rb leaks.
Another way to solve this would be set this obj->dma_buf again in
drm_gem_prime_handle_to_fd(), which would make sure obj->dma_buf is
valid in all current paths lead to drm_prime_add_buf_handle().
Regards,
Christian.
But of cause this can be fixed in other way:
+++ b/drivers/gpu/drm/drm_gem.c
@@ -180,6 +180,9 @@ drm_gem_remove_prime_handles(struct
drm_gem_object *obj, struct drm_file *filp)
drm_prime_remove_buf_handle_locked(&filp->prime,
obj->dma_buf);
}
+ if (obj->import_attach)
+ drm_prime_remove_buf_handle_locked(&filp->prime,
+ obj->import_attach->dmabuf);
mutex_unlock(&filp->prime.lock);
}
So this is pretty much a clear NAK to this patch since it shouldn't
be necessary or something is seriously broken somewhere else.
Regards,
Christian.
Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
---
Changes in v2:
Fix a typo of rbtree.
drivers/gpu/drm/drm_gem.c | 17 +----------------
drivers/gpu/drm/drm_internal.h | 4 ++--
drivers/gpu/drm/drm_prime.c | 20 ++++++++++++--------
3 files changed, 15 insertions(+), 26 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index eb0c2d041f13..ed39da383570 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -168,21 +168,6 @@ void drm_gem_private_object_init(struct
drm_device *dev,
}
EXPORT_SYMBOL(drm_gem_private_object_init);
-static void
-drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct
drm_file *filp)
-{
- /*
- * Note: obj->dma_buf can't disappear as long as we still hold a
- * handle reference in obj->handle_count.
- */
- mutex_lock(&filp->prime.lock);
- if (obj->dma_buf) {
- drm_prime_remove_buf_handle_locked(&filp->prime,
- obj->dma_buf);
- }
- mutex_unlock(&filp->prime.lock);
-}
-
/**
* drm_gem_object_handle_free - release resources bound to
userspace handles
* @obj: GEM object to clean up.
@@ -253,7 +238,7 @@ drm_gem_object_release_handle(int id, void
*ptr, void *data)
if (obj->funcs->close)
obj->funcs->close(obj, file_priv);
- drm_gem_remove_prime_handles(obj, file_priv);
+ drm_prime_remove_buf_handle(&file_priv->prime, id);
drm_vma_node_revoke(&obj->vma_node, file_priv);
drm_gem_object_handle_put_unlocked(obj);
diff --git a/drivers/gpu/drm/drm_internal.h
b/drivers/gpu/drm/drm_internal.h
index 1fbbc19f1ac0..7bb98e6a446d 100644
--- a/drivers/gpu/drm/drm_internal.h
+++ b/drivers/gpu/drm/drm_internal.h
@@ -74,8 +74,8 @@ int drm_prime_fd_to_handle_ioctl(struct
drm_device *dev, void *data,
void drm_prime_init_file_private(struct drm_prime_file_private
*prime_fpriv);
void drm_prime_destroy_file_private(struct
drm_prime_file_private *prime_fpriv);
-void drm_prime_remove_buf_handle_locked(struct
drm_prime_file_private *prime_fpriv,
- struct dma_buf *dma_buf);
+void drm_prime_remove_buf_handle(struct drm_prime_file_private
*prime_fpriv,
+ uint32_t handle);
/* drm_drv.c */
struct drm_minor *drm_minor_acquire(unsigned int minor_id);
diff --git a/drivers/gpu/drm/drm_prime.c
b/drivers/gpu/drm/drm_prime.c
index e3f09f18110c..bd5366b16381 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -190,29 +190,33 @@ static int
drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpri
return -ENOENT;
}
-void drm_prime_remove_buf_handle_locked(struct
drm_prime_file_private *prime_fpriv,
- struct dma_buf *dma_buf)
+void drm_prime_remove_buf_handle(struct drm_prime_file_private
*prime_fpriv,
+ uint32_t handle)
{
struct rb_node *rb;
- rb = prime_fpriv->dmabufs.rb_node;
+ mutex_lock(&prime_fpriv->lock);
+
+ rb = prime_fpriv->handles.rb_node;
while (rb) {
struct drm_prime_member *member;
- member = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
- if (member->dma_buf == dma_buf) {
+ member = rb_entry(rb, struct drm_prime_member, handle_rb);
+ if (member->handle == handle) {
rb_erase(&member->handle_rb, &prime_fpriv->handles);
rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);
- dma_buf_put(dma_buf);
+ dma_buf_put(member->dma_buf);
kfree(member);
- return;
- } else if (member->dma_buf < dma_buf) {
+ break;
+ } else if (member->handle < handle) {
rb = rb->rb_right;
} else {
rb = rb->rb_left;
}
}
+
+ mutex_unlock(&prime_fpriv->lock);
}
void drm_prime_init_file_private(struct drm_prime_file_private
*prime_fpriv)