[PATCH] drm/i915: Remove tautological compare in eb_relocate_vma

From: Nathan Chancellor
Date: Sat Nov 23 2019 - 14:54:47 EST

-Wtautological-compare was recently added to -Wall in LLVM, which
exposed an if statement in i915 that is always false:

../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1485:22: warning:
result of comparison of constant 576460752303423487 with expression of
type 'unsigned int' is always false
if (unlikely(remain > N_RELOC(ULONG_MAX)))

Since remain is an unsigned int, it can never be larger than UINT_MAX,
which is less than ULONG_MAX / sizeof(struct drm_i915_gem_relocation_entry).
Remove this statement to fix the warning.

Fixes: 2889caa92321 ("drm/i915: Eliminate lots of iterations over the execobjects array")
Link: https://github.com/ClangBuiltLinux/linux/issues/778
Link: https://github.com/llvm/llvm-project/commit/9740f9f0b6e5d7d5104027aee7edc9c5202dd052
Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

NOTE: Another possible fix for this is to change ULONG_MAX to UINT_MAX
but I am not sure that is what was intended by this check. I'm
happy to respin if that is the case.

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index f0998f1225af..9ed4379b4bc8 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1482,8 +1482,6 @@ static int eb_relocate_vma(struct i915_execbuffer *eb, struct i915_vma *vma)

urelocs = u64_to_user_ptr(entry->relocs_ptr);
remain = entry->relocation_count;
- if (unlikely(remain > N_RELOC(ULONG_MAX)))
- return -EINVAL;

* We must check that the entire relocation array is safe