On Wed, Oct 7, 2020 at 11:37 PM John Hubbard jhubbard@nvidia.com wrote:
On 10/7/20 2:32 PM, Daniel Vetter wrote:
On Wed, Oct 7, 2020 at 10:33 PM John Hubbard jhubbard@nvidia.com wrote:
On 10/7/20 9:44 AM, Daniel Vetter wrote:
...
@@ -398,15 +399,11 @@ static void g2d_userptr_put_dma_addr(struct g2d_data *g2d, dma_unmap_sgtable(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt, DMA_BIDIRECTIONAL, 0);
pages = frame_vector_pages(g2d_userptr->vec);if (!IS_ERR(pages)) {int i;
for (i = 0; i < g2d_userptr->npages; i++)set_page_dirty_lock(g2d_userptr->pages[i]);
for (i = 0; i < frame_vector_count(g2d_userptr->vec); i++)set_page_dirty_lock(pages[i]);}put_vaddr_frames(g2d_userptr->vec);frame_vector_destroy(g2d_userptr->vec);
unpin_user_pages(g2d_userptr->pages, g2d_userptr->npages);kvfree(g2d_userptr->pages);You can avoid writing your own loop, and just simplify the whole thing down to two lines:
unpin_user_pages_dirty_lock(g2d_userptr->pages, g2d_userptr->npages, true); kvfree(g2d_userptr->pages);Oh nice, this is neat. I'll also roll it out in the habanalabs patch, that has the same thing. Well almost, it only uses set_page_dirty, not the _lock variant. But I have no idea whether that matters or not?
It matters. And invariably, call sites that use set_page_dirty() instead of set_page_dirty_lock() were already wrong. Which is why I never had to provide anything like "unpin_user_pages_dirty (not locked)".
Although in habanalabs case, I just reviewed patch 3 and I think they *were* correctly using set_page_dirty_lock()...
Yeah I mixed that up with some other code I read, habanalabs is using _lock. I have seen a pile of gup/pup code though that only uses set_page_dirty. And looking around I did not really parse the comment above set_page_dirty(). I guess just using the _lock variant shouldn't hurt too much. I've found a comment though from the infiniband umem notifier that it's sometimes called with the page locked, and sometimes not, so life is complicated there. But how it avoids races I didn't understand. -Daniel
-- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch