From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "DRI Development" <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
kvm@vger.kernel.org, "Linux MM" <linux-mm@kvack.org>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
linux-s390@vger.kernel.org,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Inki Dae" <inki.dae@samsung.com>,
"Joonyoung Shim" <jy0922.shim@samsung.com>,
"Seung-Woo Kim" <sw0312.kim@samsung.com>,
"Kyungmin Park" <kyungmin.park@samsung.com>,
"Kukjin Kim" <kgene@kernel.org>,
"Krzysztof Kozlowski" <krzk@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Dan Williams" <dan.j.williams@intel.com>
Subject: Re: [PATCH 01/13] drm/exynos: Stop using frame_vector helpers
Date: Wed, 7 Oct 2020 23:50:47 +0200 [thread overview]
Message-ID: <CAKMK7uFgPfwxr7ePng-f=e__10+3bipmDhF4hFACcyao63m-nA@mail.gmail.com> (raw)
In-Reply-To: <895eb064-1c8f-ecfc-0a98-1fbe40cb3161@nvidia.com>
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
next prev parent reply other threads:[~2020-10-07 21:51 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 16:44 [PATCH 00/13] follow_pfn and other iomap races Daniel Vetter
2020-10-07 16:44 ` [PATCH 01/13] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-07 20:32 ` John Hubbard
2020-10-07 21:32 ` Daniel Vetter
2020-10-07 21:36 ` John Hubbard
2020-10-07 21:50 ` Daniel Vetter [this message]
2020-10-07 16:44 ` [PATCH 02/13] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-07 20:43 ` John Hubbard
2020-10-07 16:44 ` [PATCH 03/13] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-07 20:38 ` John Hubbard
2020-10-07 16:44 ` [PATCH 04/13] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-07 20:46 ` John Hubbard
2020-10-07 16:44 ` [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-07 16:53 ` Jason Gunthorpe
2020-10-07 17:12 ` Daniel Vetter
2020-10-07 17:33 ` Jason Gunthorpe
2020-10-07 21:13 ` John Hubbard
2020-10-07 21:30 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 06/13] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-07 22:18 ` John Hubbard
2020-10-07 16:44 ` [PATCH 07/13] mm: close race in generic_access_phys Daniel Vetter
2020-10-07 17:27 ` Jason Gunthorpe
2020-10-07 18:01 ` Daniel Vetter
2020-10-07 23:21 ` Jason Gunthorpe
2020-10-08 0:44 ` John Hubbard
2020-10-08 7:23 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 08/13] s390/pci: Remove races against pte updates Daniel Vetter
2020-10-08 16:44 ` Gerald Schaefer
2020-10-08 17:16 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 09/13] PCI: obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-07 18:46 ` Bjorn Helgaas
2020-10-07 16:44 ` [PATCH 10/13] PCI: revoke mappings like devmem Daniel Vetter
2020-10-07 18:41 ` Bjorn Helgaas
2020-10-07 19:24 ` Daniel Vetter
2020-10-07 19:33 ` Dan Williams
2020-10-07 19:47 ` Daniel Vetter
2020-10-07 22:23 ` Dan Williams
2020-10-07 22:29 ` Dan Williams
2020-10-08 8:09 ` Daniel Vetter
2020-10-07 23:24 ` Jason Gunthorpe
2020-10-08 7:31 ` Daniel Vetter
2020-10-08 7:49 ` Dan Williams
2020-10-08 8:13 ` Daniel Vetter
2020-10-08 8:35 ` Dan Williams
2020-10-08 12:41 ` Jason Gunthorpe
2020-10-07 16:44 ` [PATCH 11/13] mm: add unsafe_follow_pfn Daniel Vetter
2020-10-07 17:36 ` Jason Gunthorpe
2020-10-07 18:10 ` Daniel Vetter
2020-10-07 19:00 ` Jason Gunthorpe
2020-10-07 19:38 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 12/13] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-07 16:44 ` [PATCH 13/13] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-07 17:39 ` Jason Gunthorpe
2020-10-07 18:14 ` Daniel Vetter
2020-10-07 18:47 ` Jason Gunthorpe
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