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@xxxxxxxxxx> >>>> >>>> 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://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1880 . >> >> >>>> Cc: stable@xxxxxxxxxxxxxxx >>>> Signed-off-by: Michel Dänzer <mdaenzer@xxxxxxxxxx> >>>> --- >>>> 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@xxxxxxx> Thanks! AFAICT this fix can be merged now for 5.16? -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and Xwayland developer
