From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Date: Mon, 28 Nov 2022 08:18:47 +0000 Subject: Re: [PATCH mm-unstable v1 16/20] mm/frame-vector: remove FOLL_FORCE usage Message-Id: <9d0bf98a-3d6a-1082-e992-1338e1525935@redhat.com> List-Id: References: <20221116102659.70287-1-david@redhat.com> <20221116102659.70287-17-david@redhat.com> <81fb0fa3-2e06-b765-56ac-a7d981194e59@redhat.com> <08b65ac6-6786-1080-18f8-d2be109c85fc@xs4all.nl> In-Reply-To: <08b65ac6-6786-1080-18f8-d2be109c85fc@xs4all.nl> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Hans Verkuil , linux-kernel@vger.kernel.org, Andrew Morton Cc: x86@kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, Linus Torvalds , Jason Gunthorpe , John Hubbard , Peter Xu , Greg Kroah-Hartman , Andrea Arcangeli , Hugh Dickins , Nadav Amit , Vlastimil Babka , Matthew Wilcox , Mike Kravetz , Muchun Song , Shuah Khan , Lucas Stach , David Airlie , Oded Gabbay , Arnd Bergmann , Christoph Hellwig , Alex Williamson , Marek Szyprowski , Tomasz Figa , Mauro Carvalho Chehab On 28.11.22 09:17, Hans Verkuil wrote: > Hi David, > > On 27/11/2022 11:35, David Hildenbrand wrote: >> On 16.11.22 11:26, David Hildenbrand wrote: >>> FOLL_FORCE is really only for ptrace access. According to commit >>> 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are always >>> writable"), get_vaddr_frames() currently pins all pages writable as a >>> workaround for issues with read-only buffers. >>> >>> FOLL_FORCE, however, seems to be a legacy leftover as it predates >>> commit 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are >>> always writable"). Let's just remove it. >>> >>> Once the read-only buffer issue has been resolved, FOLL_WRITE could >>> again be set depending on the DMA direction. >>> >>> Cc: Hans Verkuil >>> Cc: Marek Szyprowski >>> Cc: Tomasz Figa >>> Cc: Marek Szyprowski >>> Cc: Mauro Carvalho Chehab >>> Signed-off-by: David Hildenbrand >>> --- >>>   drivers/media/common/videobuf2/frame_vector.c | 2 +- >>>   1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c >>> index 542dde9d2609..062e98148c53 100644 >>> --- a/drivers/media/common/videobuf2/frame_vector.c >>> +++ b/drivers/media/common/videobuf2/frame_vector.c >>> @@ -50,7 +50,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, >>>       start = untagged_addr(start); >>>         ret = pin_user_pages_fast(start, nr_frames, >>> -                  FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM, >>> +                  FOLL_WRITE | FOLL_LONGTERM, >>>                     (struct page **)(vec->ptrs)); >>>       if (ret > 0) { >>>           vec->got_ref = true; >> >> >> Hi Andrew, >> >> see the discussion at [1] regarding a conflict and how to proceed with >> upstreaming. The conflict would be easy to resolve, however, also >> the patch description doesn't make sense anymore with [1]. > > Might it be easier and less confusing if you post a v2 of this series > with my patch first? That way it is clear that 1) my patch has to come > first, and 2) that it is part of a single series and should be merged > by the mm subsystem. > > Less chances of things going wrong that way. > > Just mention in the v2 cover letter that the first patch was added to > make it easy to backport that fix without being hampered by merge > conflicts if it was added after your frame_vector.c patch. Yes, that's the way I would naturally do, it, however, Andrew prefers delta updates for minor changes. @Andrew, whatever you prefer! Thanks! -- Thanks, David / dhildenb