WARNING in amdgpu_sync_keep_later / dma_fence_is_later should be rate limited

[Christian König]

Am 21.09.23 um 23:30 schrieb Alex Deucher:
> On Thu, Sep 21, 2023 at 4:21 PM Rafał Miłecki <zajec5 at gmail.com> wrote:
>> On 21.09.2023 21:52, Deucher, Alexander wrote:
>>>> backporting commit 187916e6ed9d ("drm/amdgpu: install stub fence into
>>>> potential unused fence pointers") to stable kernels resulted in lots of
>>>> WARNINGs on some devices. In my case I was getting 3 WARNINGs per
>>>> second (~150 lines logged every second). Commit ended up being reverted for
>>>> stable but it exposed a potential problem. My messages log size was reaching
>>>> gigabytes and was running my /tmp/ out of space.
>>>>
>>>> Could someone take a look at amdgpu_sync_keep_later / dma_fence_is_later
>>>> and make sure its logging is rate limited to avoid such situations in the future,
>>>> please?
>>>>
>>>> Revert in linux-5.15.x:
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=li
>>>> nux-5.15.y&id=fae2d591f3cb31f722c7f065acf586830eab8c2a
>>>>
>>>> openSUSE bug report:
>>>> https://bugzilla.opensuse.org/show_bug.cgi?id=1215523
>>> These patches were never intended for stable.  They were picked up by Sasha's stable autoselect tools and automatically applied to stable kernels.
>> Are you saying massive WARNINGs in dma_fence_is_later() can't happen
>> in any other case? I understand it was an incorrect backport action but
>> I thought we may learn from it and still add some rate limit.
> All of the current places where that function is used check the
> contexts before calling it so it should be safe as is in the tree.
> That said, something like this could potentially happen again.  I
> don't think using WARN_ON_RATELIMIT() would be a problem.

Yeah, but it also shouldn't be necessary.

When this triggers you have a major driver bug at hand, spamming the 
logs is then the least of your problems.

Christian.

>
> Alex