Re: [PATCH v2 03/17] misc/habana: Stop using frame_vector helpers

[Daniel Vetter]

On Sat, Oct 10, 2020 at 11:32 PM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
>
> On Sat, Oct 10, 2020 at 10:27 PM Oded Gabbay <oded.gabbay@xxxxxxxxx> wrote:
> >
> > On Fri, Oct 9, 2020 at 10:59 AM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
> > >
> > > All we need are a pages array, pin_user_pages_fast can give us that
> > > directly. Plus this avoids the entire raw pfn side of get_vaddr_frames.
> > >
> > Thanks for the patch Daniel.
> >
> > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > > Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > > Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > > Cc: Jan Kara <jack@xxxxxxx>
> > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > > Cc: linux-mm@xxxxxxxxx
> > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-samsung-soc@xxxxxxxxxxxxxxx
> > > Cc: linux-media@xxxxxxxxxxxxxxx
> > > Cc: Oded Gabbay <oded.gabbay@xxxxxxxxx>
> > > Cc: Omer Shpigelman <oshpigelman@xxxxxxxxx>
> > > Cc: Ofir Bitton <obitton@xxxxxxxxx>
> > > Cc: Tomer Tayar <ttayar@xxxxxxxxx>
> > > Cc: Moti Haimovski <mhaimovski@xxxxxxxxx>
> > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Cc: Pawel Piskorski <ppiskorski@xxxxxxxxx>
> > > --
> > > v2: Use unpin_user_pages_dirty_lock (John)
> > > ---
> > >  drivers/misc/habanalabs/Kconfig             |  1 -
> > >  drivers/misc/habanalabs/common/habanalabs.h |  3 +-
> > >  drivers/misc/habanalabs/common/memory.c     | 49 ++++++++-------------
> > >  3 files changed, 20 insertions(+), 33 deletions(-)
> > >
> > > diff --git a/drivers/misc/habanalabs/Kconfig b/drivers/misc/habanalabs/Kconfig
> > > index 8eb5d38c618e..2f04187f7167 100644
> > > --- a/drivers/misc/habanalabs/Kconfig
> > > +++ b/drivers/misc/habanalabs/Kconfig
> > > @@ -6,7 +6,6 @@
> > >  config HABANA_AI
> > >         tristate "HabanaAI accelerators (habanalabs)"
> > >         depends on PCI && HAS_IOMEM
> > > -       select FRAME_VECTOR
> > >         select DMA_SHARED_BUFFER
> > >         select GENERIC_ALLOCATOR
> > >         select HWMON
> > > diff --git a/drivers/misc/habanalabs/common/habanalabs.h b/drivers/misc/habanalabs/common/habanalabs.h
> > > index edbd627b29d2..c1b3ad613b15 100644
> > > --- a/drivers/misc/habanalabs/common/habanalabs.h
> > > +++ b/drivers/misc/habanalabs/common/habanalabs.h
> > > @@ -881,7 +881,8 @@ struct hl_ctx_mgr {
> > >  struct hl_userptr {
> > >         enum vm_type_t          vm_type; /* must be first */
> > >         struct list_head        job_node;
> > > -       struct frame_vector     *vec;
> > > +       struct page             **pages;
> > > +       unsigned int            npages;
> > Can you please update the kerneldoc comment section of this structure
> > according to your changes ?
>
> Apologies I missed the nice kerneldoc. I'll fix that in the next round.
>
>
> > >         struct sg_table         *sgt;
> > >         enum dma_data_direction dir;
> > >         struct list_head        debugfs_list;
> > > diff --git a/drivers/misc/habanalabs/common/memory.c b/drivers/misc/habanalabs/common/memory.c
> > > index 5ff4688683fd..327b64479f97 100644
> > > --- a/drivers/misc/habanalabs/common/memory.c
> > > +++ b/drivers/misc/habanalabs/common/memory.c
> > > @@ -1281,45 +1281,41 @@ static int get_user_memory(struct hl_device *hdev, u64 addr, u64 size,
> > >                 return -EFAULT;
> > >         }
> > >
> > > -       userptr->vec = frame_vector_create(npages);
> > > -       if (!userptr->vec) {
> > > +       userptr->pages = kvmalloc_array(npages, sizeof(*userptr->pages),
> > > +                                       GFP_KERNEL);
> > > +       if (!userptr->pages) {
> > >                 dev_err(hdev->dev, "Failed to create frame vector\n");
> > >                 return -ENOMEM;
> > >         }
> > >
> > > -       rc = get_vaddr_frames(start, npages, FOLL_FORCE | FOLL_WRITE,
> > > -                               userptr->vec);
> > > +       rc = pin_user_pages_fast(start, npages, FOLL_FORCE | FOLL_WRITE,
> > > +                                userptr->pages);
> > >
> > >         if (rc != npages) {
> > >                 dev_err(hdev->dev,
> > >                         "Failed to map host memory, user ptr probably wrong\n");
> > >                 if (rc < 0)
> > > -                       goto destroy_framevec;
> > > +                       goto destroy_pages;
> > > +               npages = rc;
> > >                 rc = -EFAULT;
> > > -               goto put_framevec;
> > > -       }
> > > -
> > > -       if (frame_vector_to_pages(userptr->vec) < 0) {
> > > -               dev_err(hdev->dev,
> > > -                       "Failed to translate frame vector to pages\n");
> > > -               rc = -EFAULT;
> > > -               goto put_framevec;
> > > +               goto put_pages;
> > >         }
> > > +       userptr->npages = npages;
> > >
> > >         rc = sg_alloc_table_from_pages(userptr->sgt,
> > > -                                       frame_vector_pages(userptr->vec),
> > > -                                       npages, offset, size, GFP_ATOMIC);
> > > +                                      userptr->pages,
> > > +                                      npages, offset, size, GFP_ATOMIC);
> > I think that because the call to kvmalloc_array() is done with
> > GFP_KERNEL, there is no point in using GFP_ATOMIC here.
> > And actually, this path only needs to avoid yielding when using a
> > special debug mode.
> > So I suggest putting here GFP_KERNEL.
>
> Huh, I didn't even notice the GFP_ATOMIC here. This looks indeed
> strange and GFP_KERNEL should be perfectly fine in a function that
> also calls pin_user_pages (since that one can allocate and do worse
> stuff like userspace pagefaults).
>
> But since that GFP_ATOMIC is there already I'll do that in a separate patch.

Ok I read up on your usage of GFP_ATOMIC in habanalabs, and I'm not
going to touch this. But I'm pretty sure it's broken.

You seem to have some requirement of not allocating memory with
blocking (see hl_cb_alloc()), and that seems to be way you allocate
tons of structures with GFP_ATOMIC. There's 2 pretty tough problems
with that:
- GFP_ATOMIC can fail, even when the system hasn't run out of memory
yet. You _must_ have a fallback back to handle allocation failures for
these. Quick survey shows you a ton of GFP_ATOMIC callsites, and very
little fallback code - I've found none, but I didn't check the failure
handlers all going up the possible callchains.
- pin_user_pages can allocate memory, so you're breaking your own "no
sleeping in these paths" rules.

This isn't going to get fixed with a quick oneliner patch, depending
what's needed you're looking at a driver rearchitecture here :-/ Hence
I'm not going to touch this in the next patch, but leave it all as-is.

Cheers, Daniel

>
> > In the meanwhile, I'll run this patch (coupled with the next patch) in
> > our C/I to make sure there are no regressions.
>
> Excellent. I'll wait with v3 until that's done, just in case you hit a
> snag I need to fix.
>
> Cheers, Daniel
>
> > Thanks,
> > Oded
> >
> > >         if (rc < 0) {
> > >                 dev_err(hdev->dev, "failed to create SG table from pages\n");
> > > -               goto put_framevec;
> > > +               goto put_pages;
> > >         }
> > >
> > >         return 0;
> > >
> > > -put_framevec:
> > > -       put_vaddr_frames(userptr->vec);
> > > -destroy_framevec:
> > > -       frame_vector_destroy(userptr->vec);
> > > +put_pages:
> > > +       unpin_user_pages(userptr->pages, npages);
> > > +destroy_pages:
> > > +       kvfree(userptr->pages);
> > >         return rc;
> > >  }
> > >
> > > @@ -1405,8 +1401,6 @@ int hl_pin_host_memory(struct hl_device *hdev, u64 addr, u64 size,
> > >   */
> > >  void hl_unpin_host_memory(struct hl_device *hdev, struct hl_userptr *userptr)
> > >  {
> > > -       struct page **pages;
> > > -
> > >         hl_debugfs_remove_userptr(hdev, userptr);
> > >
> > >         if (userptr->dma_mapped)
> > > @@ -1414,15 +1408,8 @@ void hl_unpin_host_memory(struct hl_device *hdev, struct hl_userptr *userptr)
> > >                                                         userptr->sgt->nents,
> > >                                                         userptr->dir);
> > >
> > > -       pages = frame_vector_pages(userptr->vec);
> > > -       if (!IS_ERR(pages)) {
> > > -               int i;
> > > -
> > > -               for (i = 0; i < frame_vector_count(userptr->vec); i++)
> > > -                       set_page_dirty_lock(pages[i]);
> > > -       }
> > > -       put_vaddr_frames(userptr->vec);
> > > -       frame_vector_destroy(userptr->vec);
> > > +       unpin_user_pages_dirty_lock(userptr->pages, userptr->npages, true);
> > > +       kvfree(userptr->pages);
> > >
> > >         list_del(&userptr->job_node);
> > >
> > > --
> > > 2.28.0
> > >
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch