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Wed, 07 Oct 2020 14:50:59 -0700 (PDT) MIME-Version: 1.0 References: <20201007164426.1812530-1-daniel.vetter@ffwll.ch> <20201007164426.1812530-2-daniel.vetter@ffwll.ch> <80718789-b3de-c30a-03c5-7c8cbf41f7d9@nvidia.com> <895eb064-1c8f-ecfc-0a98-1fbe40cb3161@nvidia.com> In-Reply-To: <895eb064-1c8f-ecfc-0a98-1fbe40cb3161@nvidia.com> From: Daniel Vetter Date: Wed, 7 Oct 2020 23:50:47 +0200 Message-ID: Subject: Re: [PATCH 01/13] drm/exynos: Stop using frame_vector helpers To: John Hubbard Cc: DRI Development , LKML , kvm@vger.kernel.org, Linux MM , Linux ARM , linux-samsung-soc , "open list:DMA BUFFER SHARING FRAMEWORK" , linux-s390@vger.kernel.org, Daniel Vetter , Jason Gunthorpe , Inki Dae , Joonyoung Shim , Seung-Woo Kim , Kyungmin Park , Kukjin Kim , Krzysztof Kozlowski , Andrew Morton , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jan Kara , Dan Williams Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Oct 7, 2020 at 11:37 PM John Hubbard wrote: > > On 10/7/20 2:32 PM, Daniel Vetter wrote: > > On Wed, Oct 7, 2020 at 10:33 PM John Hubbard 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