From: "Christian König" <christian.koenig@amd.com>
To: "Michel Dänzer" <michel@daenzer.net>,
"Christian König" <ckoenig.leichtzumerken@gmail.com>
Cc: linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org,
dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org
Subject: Re: [Linaro-mm-sig] [PATCH] dma-buf/poll: Get a file reference for outstanding fence callbacks
Date: Thu, 4 Nov 2021 09:20:40 +0100 [thread overview]
Message-ID: <c0265dc9-15c4-e838-f183-3e9b82a6ff50@amd.com> (raw)
In-Reply-To: <20cfea36-a8cc-7bd1-9604-57efdf4710e2@daenzer.net>
Am 03.11.21 um 15:50 schrieb Michel Dänzer:
> On 2021-07-23 10:22, Christian König wrote:
>> Am 23.07.21 um 10:19 schrieb Michel Dänzer:
>>> On 2021-07-23 10:04 a.m., Christian König wrote:
>>>> Am 23.07.21 um 09:58 schrieb Michel Dänzer:
>>>>> From: Michel Dänzer <mdaenzer@redhat.com>
>>>>>
>>>>> This makes sure we don't hit the
>>>>>
>>>>> BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active);
>>>>>
>>>>> in dma_buf_release, which could be triggered by user space closing the
>>>>> dma-buf file description while there are outstanding fence callbacks
>>>>> from dma_buf_poll.
>>>> I was also wondering the same thing while working on this, but then thought that the poll interface would take care of this.
>>> I was able to hit the BUG_ON with https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.gnome.org%2FGNOME%2Fmutter%2F-%2Fmerge_requests%2F1880&data=04%7C01%7Cchristian.koenig%40amd.com%7C8d930ab39011481a839c08d99ed95755%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637715479787056688%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=SjxSZIsWkP7ru1iHyL0IY9hN9882ENv7Cy38vzOtqyc%3D&reserved=0 .
>>>
>>>
>>>>> Cc: stable@vger.kernel.org
>>>>> Signed-off-by: Michel Dänzer <mdaenzer@redhat.com>
>>>>> ---
>>>>> drivers/dma-buf/dma-buf.c | 18 ++++++++++++------
>>>>> 1 file changed, 12 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>>>>> index 6c520c9bd93c..ec25498a971f 100644
>>>>> --- a/drivers/dma-buf/dma-buf.c
>>>>> +++ b/drivers/dma-buf/dma-buf.c
>>>>> @@ -65,12 +65,9 @@ static void dma_buf_release(struct dentry *dentry)
>>>>> BUG_ON(dmabuf->vmapping_counter);
>>>>> /*
>>>>> - * Any fences that a dma-buf poll can wait on should be signaled
>>>>> - * before releasing dma-buf. This is the responsibility of each
>>>>> - * driver that uses the reservation objects.
>>>>> - *
>>>>> - * If you hit this BUG() it means someone dropped their ref to the
>>>>> - * dma-buf while still having pending operation to the buffer.
>>>>> + * If you hit this BUG() it could mean:
>>>>> + * * There's a file reference imbalance in dma_buf_poll / dma_buf_poll_cb or somewhere else
>>>>> + * * dmabuf->cb_in/out.active are non-0 despite no pending fence callback
>>>>> */
>>>>> BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active);
>>>>> @@ -196,6 +193,7 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
>>>>> static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
>>>>> {
>>>>> struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
>>>>> + struct dma_buf *dmabuf = container_of(dcb->poll, struct dma_buf, poll);
>>>>> unsigned long flags;
>>>>> spin_lock_irqsave(&dcb->poll->lock, flags);
>>>>> @@ -203,6 +201,8 @@ static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
>>>>> dcb->active = 0;
>>>>> spin_unlock_irqrestore(&dcb->poll->lock, flags);
>>>>> dma_fence_put(fence);
>>>>> + /* Paired with get_file in dma_buf_poll */
>>>>> + fput(dmabuf->file);
>>>> Is calling fput() in interrupt context ok? IIRC that could potentially sleep.
>>> Looks fine AFAICT: It has
>>>
>>> if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
>>>
>>> and as a fallback for that, it adds the file to a lock-less delayed_fput_list which is processed by a workqueue.
>> Ah, yes that makes sense.
>>
>> Fell free to add Reviewed-by: Christian König <christian.koenig@amd.com>
> Thanks! AFAICT this fix can be merged now for 5.16?
I've just pushed it to drm-misc-next-fixes since it won't even apply to
drm-misc-fixes.
Could be that we get requests to backport this because of the CC stable.
Christian.
next prev parent reply other threads:[~2021-11-04 8:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-23 7:58 [PATCH] dma-buf/poll: Get a file reference for outstanding fence callbacks Michel Dänzer
2021-07-23 8:04 ` Christian König
2021-07-23 8:19 ` Michel Dänzer
2021-07-23 8:22 ` [Linaro-mm-sig] " Christian König
2021-11-03 14:50 ` Michel Dänzer
2021-11-04 8:20 ` Christian König [this message]
2021-07-23 9:02 ` Daniel Vetter
2021-07-23 9:11 ` Michel Dänzer
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