Re: [PATCH] [v2] drm/i915: Check for get_pages instead of shmem (filp)

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On 10/02/16 17:39, Ben Widawsky wrote:
On Wed, Feb 10, 2016 at 04:23:08PM +0000, Chris Wilson wrote:
On Wed, Feb 10, 2016 at 07:42:23AM -0800, Ben Widawsky wrote:
Do you guys get the CI mails? This version has regressions. v1 did not. I don't
know what to trust.

I didn't even see v2 itself!

On Tue, Feb 09, 2016 at 11:44:12AM -0800, Ben Widawsky wrote:
This behavior of checking for a shmem backed GEM object was introduced here:
commit 4c914c0c7c787b8f730128a8cdcca9c50b0784ab
Author: Brad Volkin <bradley.d.volkin@xxxxxxxxx>
Date:   Tue Feb 18 10:15:45 2014 -0800

     drm/i915: Refactor shmem pread setup

It is possible for an object to not be a shmem backed GEM object (for example
userptr objects). An example of how we hit this failure can be found through
copy_batch() in the command parser because we allocate a userptr object for the
batch which contains privileged instructions. Userptr calls
drm_gem_private_object_init() which explicitly sets the filp to none.

NOTE: I manually retyped this from a test machine. So I haven't even compiled
this exact patch.

v2: Use same logic as from a2a4f916c2f (Kristian, Dave Gordon)

Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Kristian Høgsberg <krh@xxxxxxxxxxxxx>
Cc: Dave Gordon <david.s.gordon@xxxxxxxxx>
Signed-off-by: Ben Widawsky <benjamin.widawsky@xxxxxxxxx>
Tested-by: Jordan Justen <jordan.l.justen@xxxxxxxxx> (v1)
Reviewed-by: Jordan Justen <jordan.l.justen@xxxxxxxxx> (v1)

---
  drivers/gpu/drm/i915/i915_gem.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index e9b19bc..7fd79b0 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -489,7 +489,7 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,

  	*needs_clflush = 0;

-	if (!obj->base.filp)
+	if (WARN_ON((obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE) == 0))

It looks like the above code can't be reached? 'filp' is tested in i915_gem_pread_ioctl(), before i915_gem_obj_prepare_shmem_read() is called!

Don't use WARN_ON, there is code (or will be) where we use
prepare_shmem_read/write to determine if we can use the shmem paths.

Also i915_gem_obj_prepare_shmem_write() requires the same treatment.

No such function, but there's a 'filp' test in i915_gem_pwrite_ioctl().

Also, what about i915_gem_mmap_ioctl() ? Is mmap() also going to be legitimate without a file pointer?

> My apologies I had this patch but appear to have accidentally squashed
it whilst rebasing. Thanks!
-Chris

So... is someone going to land this fix? We need it.

Looks like Chris wants this to read

    if (!(obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE))
        return -EINVAL;

leaving it to the caller to decide whether to log a complaint.
I'm happy with that.

.Dave.
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