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. -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer
