On Fri, Jul 23, 2021 at 10:19:49AM +0200, Michel Dänzer wrote: > 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 . igt test would be really lovely. Maybe base something off the import/export igts from Jason? -Daniel > > > >> 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 -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
