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,
Christian.
