From: Mauro Carvalho Chehab <mchehab@s-opensource.com> To: Dan Williams <dan.j.williams@intel.com> Cc: akpm@linux-foundation.org, Jan Kara <jack@suse.cz>, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab <mchehab@kernel.org>, linux-media@vger.kernel.org Subject: Re: [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support Date: Tue, 7 Nov 2017 06:33:45 -0200 [thread overview] Message-ID: <20171107063345.22626a5d@vento.lan> (raw) In-Reply-To: <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> Em Mon, 06 Nov 2017 16:57:28 -0800 Dan Williams <dan.j.williams@intel.com> escreveu: > V4L2 memory registrations are incompatible with filesystem-dax that > needs the ability to revoke dma access to a mapping at will, or > otherwise allow the kernel to wait for completion of DMA. The > filesystem-dax implementation breaks the traditional solution of > truncate of active file backed mappings since there is no page-cache > page we can orphan to sustain ongoing DMA. > > If v4l2 wants to support long lived DMA mappings it needs to arrange to > hold a file lease or use some other mechanism so that the kernel can > coordinate revoking DMA access when the filesystem needs to truncate > mappings. Not sure if I understand this your comment here... what happens if FS_DAX is enabled? The new err = get_user_pages_longterm() would cause DMA allocation to fail? If so, that doesn't sound right. Instead, mm should somehow mark this mapping to be out of FS_DAX control range. Also, it is not only videobuf-dma-sg.c that does long lived DMA mappings. VB2 also does that (and videobuf-vmalloc). Regards, Mauro > > Reported-by: Jan Kara <jack@suse.cz> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > Cc: linux-media@vger.kernel.org > Cc: <stable@vger.kernel.org> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > --- > drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c > index 0b5c43f7e020..f412429cf5ba 100644 > --- a/drivers/media/v4l2-core/videobuf-dma-sg.c > +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c > @@ -185,12 +185,13 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, > dprintk(1, "init user [0x%lx+0x%lx => %d pages]\n", > data, size, dma->nr_pages); > > - err = get_user_pages(data & PAGE_MASK, dma->nr_pages, > + err = get_user_pages_longterm(data & PAGE_MASK, dma->nr_pages, > flags, dma->pages, NULL); > > if (err != dma->nr_pages) { > dma->nr_pages = (err >= 0) ? err : 0; > - dprintk(1, "get_user_pages: err=%d [%d]\n", err, dma->nr_pages); > + dprintk(1, "get_user_pages_longterm: err=%d [%d]\n", err, > + dma->nr_pages); > return err < 0 ? err : -EINVAL; > } > return 0; > Thanks, Mauro
WARNING: multiple messages have this Message-ID (diff)
From: Mauro Carvalho Chehab <mchehab@s-opensource.com> To: Dan Williams <dan.j.williams@intel.com> Cc: akpm@linux-foundation.org, Jan Kara <jack@suse.cz>, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab <mchehab@kernel.org>, linux-media@vger.kernel.org Subject: Re: [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support Date: Tue, 7 Nov 2017 06:33:45 -0200 [thread overview] Message-ID: <20171107063345.22626a5d@vento.lan> (raw) In-Reply-To: <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> Em Mon, 06 Nov 2017 16:57:28 -0800 Dan Williams <dan.j.williams@intel.com> escreveu: > V4L2 memory registrations are incompatible with filesystem-dax that > needs the ability to revoke dma access to a mapping at will, or > otherwise allow the kernel to wait for completion of DMA. The > filesystem-dax implementation breaks the traditional solution of > truncate of active file backed mappings since there is no page-cache > page we can orphan to sustain ongoing DMA. > > If v4l2 wants to support long lived DMA mappings it needs to arrange to > hold a file lease or use some other mechanism so that the kernel can > coordinate revoking DMA access when the filesystem needs to truncate > mappings. Not sure if I understand this your comment here... what happens if FS_DAX is enabled? The new err = get_user_pages_longterm() would cause DMA allocation to fail? If so, that doesn't sound right. Instead, mm should somehow mark this mapping to be out of FS_DAX control range. Also, it is not only videobuf-dma-sg.c that does long lived DMA mappings. VB2 also does that (and videobuf-vmalloc). Regards, Mauro > > Reported-by: Jan Kara <jack@suse.cz> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > Cc: linux-media@vger.kernel.org > Cc: <stable@vger.kernel.org> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > --- > drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c > index 0b5c43f7e020..f412429cf5ba 100644 > --- a/drivers/media/v4l2-core/videobuf-dma-sg.c > +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c > @@ -185,12 +185,13 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, > dprintk(1, "init user [0x%lx+0x%lx => %d pages]\n", > data, size, dma->nr_pages); > > - err = get_user_pages(data & PAGE_MASK, dma->nr_pages, > + err = get_user_pages_longterm(data & PAGE_MASK, dma->nr_pages, > flags, dma->pages, NULL); > > if (err != dma->nr_pages) { > dma->nr_pages = (err >= 0) ? err : 0; > - dprintk(1, "get_user_pages: err=%d [%d]\n", err, dma->nr_pages); > + dprintk(1, "get_user_pages_longterm: err=%d [%d]\n", err, > + dma->nr_pages); > return err < 0 ? err : -EINVAL; > } > return 0; > Thanks, Mauro -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-11-07 8:33 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-07 0:57 [PATCH 0/3] introduce get_user_pages_longterm() Dan Williams 2017-11-07 0:57 ` Dan Williams 2017-11-07 0:57 ` [PATCH 1/3] mm: introduce get_user_pages_longterm Dan Williams 2017-11-07 0:57 ` Dan Williams 2017-11-10 9:01 ` Christoph Hellwig 2017-11-10 9:01 ` Christoph Hellwig 2017-11-07 0:57 ` [PATCH 2/3] IB/core: disable memory registration of fileystem-dax vmas Dan Williams 2017-11-07 0:57 ` Dan Williams [not found] ` <151001624138.16354.16836728315400060928.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org> 2017-11-10 9:01 ` Christoph Hellwig 2017-11-10 9:01 ` Christoph Hellwig 2017-11-10 9:01 ` Christoph Hellwig 2017-11-07 0:57 ` [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support Dan Williams 2017-11-07 0:57 ` Dan Williams 2017-11-07 8:33 ` Mauro Carvalho Chehab [this message] 2017-11-07 8:33 ` Mauro Carvalho Chehab 2017-11-07 17:43 ` Dan Williams 2017-11-07 17:43 ` Dan Williams 2017-11-07 20:39 ` Mauro Carvalho Chehab 2017-11-07 20:39 ` Mauro Carvalho Chehab 2017-11-08 0:13 ` Dan Williams 2017-11-08 0:13 ` Dan Williams
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