Messages in this thread | | | Subject | Re: [Linaro-mm-sig] [PATCH] dma-buf/poll: Get a file reference for outstanding fence callbacks | From | Christian König <> | Date | Thu, 4 Nov 2021 09:20:40 +0100 |
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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.
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