* Re: [PATCH] drm/amdgpu: Fix double free in amdgpu_get_xgmi_hive
2022-01-20 10:17 [PATCH] drm/amdgpu: Fix double free in amdgpu_get_xgmi_hive Miaoqian Lin
@ 2022-01-20 18:04 ` Felix Kuehling
0 siblings, 0 replies; 2+ messages in thread
From: Felix Kuehling @ 2022-01-20 18:04 UTC (permalink / raw)
To: Miaoqian Lin, Alex Deucher, Christian König, Pan, Xinhui,
David Airlie, Daniel Vetter, Hawking Zhang, John Clements,
Jonathan Kim, Bernard Zhao, Kevin Wang, shaoyunl, Tian Tao,
amd-gfx, dri-devel, linux-kernel
Am 2022-01-20 um 5:17 a.m. schrieb Miaoqian Lin:
> Callback function amdgpu_xgmi_hive_release() in kobject_put()
> calls kfree(hive), So we don't need call kfree(hive) again.
>
> Fixes: 7b833d680481 ("drm/amd/amdgpu: fix potential memleak")
> Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
The patch is
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
This kobject_init_and_add error handling semantics is very unintuitive,
and we keep stumbling over it. I wonder is there is a better way to
handle this. Basically, this is what it looks like, when done correctly:
foo = kzalloc(sizeof(*foo), GFP_KERNEL);
if (!foo)
return -ENOMEM;
r = kobject_init_and_add(&foo->kobj, &foo_type, &parent, "foo_name");
if (r) {
/* OK, initialization failed, but I still need to
* clean up manually as if the call had succeeded.
*/
kobject_put(&foo->kobj);
/* Don't kfree foo, because that's already done by
* a callback setup by the call that failed above.
*/
return r;
}
Given that unintuitive behaviour, I'd argue that kobject_init_and_add
fails as an abstraction. Code would be clearer, more intuitive and safer
by calling kobject_init and kobject_add separately itself.
kobject_init_and_add saves you typing exactly one line of code, and it's
just not worth it:
foo = kzalloc(sizeof(*foo), GFP_KERNEL);
if (!foo)
return -ENOMEM;
kobject_init(&foo->kobj, &foo_type); /* never fails */
r = kobject_add(&foo->kobj, &parent, "foo_name");
if (r) {
/* since kobj_init succeeded, it's obvious that kobj_put
* is the right thing to do to handle all the cleanup.
*/
kobject_put(&foo->kobj);
return r;
}
Regards,
Felix
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
> index e8b8f28c2f72..35d4b966ef2c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
> @@ -393,7 +393,6 @@ struct amdgpu_hive_info *amdgpu_get_xgmi_hive(struct amdgpu_device *adev)
> if (ret) {
> dev_err(adev->dev, "XGMI: failed initializing kobject for xgmi hive\n");
> kobject_put(&hive->kobj);
> - kfree(hive);
> hive = NULL;
> goto pro_end;
> }
^ permalink raw reply [flat|nested] 2+ messages in thread