<!DOCTYPE html><html><head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body> Am 17.12.24 um 12:06 schrieb Wei Lin Guay: <blockquote type="cite" cite="mid:C369F330-5BAD-4AC6-A13C-EEABD29F2F08@meta.com">[SNIP] <blockquote type="cite"> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""></pre> </blockquote> <pre class="moz-quote-pre" wrap=""> Please send that out once more with me on explicit CC. </pre> </blockquote> <pre class="moz-quote-pre" wrap=""> I will resend the patch series. I was experiencing issues with my email client, which inadvertently split the series into two separate emails.</pre> </blockquote> Alternatively I can also copy the code from the list archive and explain why that doesn't work: +void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked) +{ + struct vfio_pci_dma_buf *priv; + struct vfio_pci_dma_buf *tmp; + + lockdep_assert_held_write(&vdev->memory_lock); This makes sure that the caller is holding vdev->memory_lock. + + list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) { + if (!dma_buf_try_get(priv->dmabuf)) This here only works because vfio_pci_dma_buf_release() also grabs vdev->memory_lock and so we are protected against concurrent releases. + continue; + if (priv->revoked != revoked) { + dma_resv_lock(priv->dmabuf->resv, NULL); + priv->revoked = revoked; + dma_buf_move_notify(priv->dmabuf); + dma_resv_unlock(priv->dmabuf->resv); + } + dma_buf_put(priv->dmabuf); The problem is now that this here might drop the last reference which in turn calls vfio_pci_dma_buf_release() which also tries to grab vdev->memory_lock and so results in a deadlock. + } +} This pattern was suggested multiple times and I had to rejected it every time because the whole idea is just fundamentally broken. It's really astonishing how people always come up with the same broken pattern. Regards, Christian. <blockquote type="cite" cite="mid:C369F330-5BAD-4AC6-A13C-EEABD29F2F08@meta.com"> <pre class="moz-quote-pre" wrap=""> </pre> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""> Apart from that I have to reject the adding of dma_buf_try_get(), that is clearly not something we should do. </pre> </blockquote> <pre class="moz-quote-pre" wrap=""> Understood. It appears that Vivek has confirmed that his v2 has resolved the issue. I will follow up with him to determine if he plans to resume his patch, and if so, I will apply my last patch on top of his updated patch series Thanks, Wei Lin </pre> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""> Thanks, Christian. </pre> </blockquote> <pre class="moz-quote-pre" wrap=""> </pre> </blockquote> </body> </html>