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 | Fri, 23 Jul 2021 10:22:34 +0200 |
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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://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1880 . > > >>> 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, Christian.
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