[PATCH v2] drm/amd/display: Increase frame warning limit with KASAN or KCSAN in dml2

From: Nathan Chancellor <nathan@kernel.org>
To: harry.wentland@amd.com, sunpeng.li@amd.com,
	Rodrigo.Siqueira@amd.com,  alexander.deucher@amd.com,
	christian.koenig@amd.com, Xinhui.Pan@amd.com
Cc: trix@redhat.com, llvm@lists.linux.dev, ndesaulniers@google.com,
	patches@lists.linux.dev, dri-devel@lists.freedesktop.org,
	Nathan Chancellor <nathan@kernel.org>,
	amd-gfx@lists.freedesktop.org
Subject: [PATCH v2] drm/amd/display: Increase frame warning limit with KASAN or KCSAN in dml2
Date: Thu, 02 Nov 2023 10:40:52 -0700	[thread overview]
Message-ID: <20231102-amdgpu-dml2-increase-frame-size-warning-for-clang-v2-1-b088a718131a@kernel.org> (raw)

When building ARCH=x86_64 allmodconfig with clang, which will typically
have sanitizers enabled, there is a warning about a large stack frame.

  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c:6265:13: error: stack frame size (2520) exceeds limit (2048) in 'dml_prefetch_check' [-Werror,-Wframe-larger-than]
   6265 | static void dml_prefetch_check(struct display_mode_lib_st *mode_lib)
        |             ^
  1 error generated.

Notably, GCC 13.2.0 does not do too much of a better job, as it is right
at the current limit of 2048 (and others have reported being over with
older GCC versions):

  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c: In function 'dml_prefetch_check':
  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c:6705:1: error: the frame size of 2048 bytes is larger than 1800 bytes [-Werror=frame-larger-than=]
   6705 | }
        | ^

In the past, these warnings have been avoided by reducing the number of
parameters to various functions so that not as many arguments need to be
passed on the stack. However, these patches take a good amount of effort
to write despite being mechanical due to code structure and complexity
and they are never carried forward to new generations of the code so
that effort has to be expended every new hardware generation, which
becomes harder to justify as time goes on.

To avoid having a noticeable or lengthy breakage in all{mod,yes}config,
which are easy testing targets that have -Werror enabled, increase the
limit for configurations that have KASAN or KCSAN enabled by 50% so that
cases of extremely poor code generation can still be caught while not
breaking the majority of builds. CONFIG_KMSAN also causes high stack
usage but the frame limit is already set to zero when it is enabled,
which is accounted for by the check for CONFIG_FRAME_WARN=0 in the dml2
Makefile.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
If there is another DRM pull before 6.7-rc1, it would be much
appreciated if this could make that so that other trees are not
potentially broken by this. If not, no worries, as it was my fault for
not sending this sooner.

Changes in v2:
- Adjust workaround to check for either CONFIG_KASAN=y or
  CONFIG_KCSAN=y, as the same problem has been reported with older
  versions of GCC (Hamza, Alex)
- Link to v1: https://lore.kernel.org/r/20231102-amdgpu-dml2-increase-frame-size-warning-for-clang-v1-1-6eb157352931@kernel.org
---
 drivers/gpu/drm/amd/display/dc/dml2/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dml2/Makefile b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
index 70ae5eba624e..acff3449b8d7 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
@@ -60,8 +60,12 @@ endif
 endif
 
 ifneq ($(CONFIG_FRAME_WARN),0)
+ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
+frame_warn_flag := -Wframe-larger-than=3072
+else
 frame_warn_flag := -Wframe-larger-than=2048
 endif
+endif
 
 CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_core.o := $(dml2_ccflags) $(frame_warn_flag)
 CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_util.o := $(dml2_ccflags)

---
base-commit: 21e80f3841c01aeaf32d7aee7bbc87b3db1aa0c6
change-id: 20231102-amdgpu-dml2-increase-frame-size-warning-for-clang-c93bd2d6a871

Best regards,
-- 
Nathan Chancellor <nathan@kernel.org>

