Re: [PATCH] drm/i915: Mark expected switch fall-throughs

From: Kees Cook
Date: Mon Jul 22 2019 - 14:24:11 EST

On Mon, Jul 22, 2019 at 01:12:44PM -0500, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.
>
> This patch fixes the following warnings:
>
> drivers/gpu/drm/i915/gem/i915_gem_mman.c: In function âi915_gem_faultâ:
> drivers/gpu/drm/i915/gem/i915_gem_mman.c:342:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
> if (!i915_terminally_wedged(i915))
> ^
> drivers/gpu/drm/i915/gem/i915_gem_mman.c:345:2: note: here
> case -EAGAIN:
> ^~~~
>
> drivers/gpu/drm/i915/gem/i915_gem_pages.c: In function âi915_gem_object_mapâ:
> ./include/linux/compiler.h:78:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
> # define unlikely(x) __builtin_expect(!!(x), 0)
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/asm-generic/bug.h:136:2: note: in expansion of macro âunlikelyâ
> unlikely(__ret_warn_on); \
> ^~~~~~~~
> drivers/gpu/drm/i915/i915_utils.h:49:25: note: in expansion of macro âWARNâ
> #define MISSING_CASE(x) WARN(1, "Missing case (%s == %ld)\n", \
> ^~~~
> drivers/gpu/drm/i915/gem/i915_gem_pages.c:270:3: note: in expansion of macro âMISSING_CASEâ
> MISSING_CASE(type);
> ^~~~~~~~~~~~
> drivers/gpu/drm/i915/gem/i915_gem_pages.c:272:2: note: here
> case I915_MAP_WB:
> ^~~~
>
> drivers/gpu/drm/i915/i915_gpu_error.c: In function âerror_record_engine_registersâ:
> ./include/linux/compiler.h:78:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
> # define unlikely(x) __builtin_expect(!!(x), 0)
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/asm-generic/bug.h:136:2: note: in expansion of macro âunlikelyâ
> unlikely(__ret_warn_on); \
> ^~~~~~~~
> drivers/gpu/drm/i915/i915_utils.h:49:25: note: in expansion of macro âWARNâ
> #define MISSING_CASE(x) WARN(1, "Missing case (%s == %ld)\n", \
> ^~~~
> drivers/gpu/drm/i915/i915_gpu_error.c:1196:5: note: in expansion of macro âMISSING_CASEâ
> MISSING_CASE(engine->id);
> ^~~~~~~~~~~~
> drivers/gpu/drm/i915/i915_gpu_error.c:1197:4: note: here
> case RCS0:
> ^~~~
>
> drivers/gpu/drm/i915/display/intel_dp.c: In function âintel_dp_get_fia_supported_lane_countâ:
> ./include/linux/compiler.h:78:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
> # define unlikely(x) __builtin_expect(!!(x), 0)
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/asm-generic/bug.h:136:2: note: in expansion of macro âunlikelyâ
> unlikely(__ret_warn_on); \
> ^~~~~~~~
> drivers/gpu/drm/i915/i915_utils.h:49:25: note: in expansion of macro âWARNâ
> #define MISSING_CASE(x) WARN(1, "Missing case (%s == %ld)\n", \
> ^~~~
> drivers/gpu/drm/i915/display/intel_dp.c:233:3: note: in expansion of macro âMISSING_CASEâ
> MISSING_CASE(lane_info);
> ^~~~~~~~~~~~
> drivers/gpu/drm/i915/display/intel_dp.c:234:2: note: here
> case 1:
> ^~~~
>
> drivers/gpu/drm/i915/display/intel_display.c: In function âcheck_digital_port_conflictsâ:
> CC [M] drivers/gpu/drm/nouveau/nvkm/engine/disp/cursgv100.o
> drivers/gpu/drm/i915/display/intel_display.c:12043:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
> if (WARN_ON(!HAS_DDI(to_i915(dev))))
> ^
> drivers/gpu/drm/i915/display/intel_display.c:12046:3: note: here
> case INTEL_OUTPUT_DP:
> ^~~~
>
> Also, notice that the Makefile is modified in order to stop
> ignoring fall-through warnings. The -Wimplicit-fallthrough
> option will be enabled globally in v5.3.
>
> Warning level 3 was used: -Wimplicit-fallthrough=3
>
> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

Excellent; I think these are literally the last remaining cases in the
kernel. :)

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
> drivers/gpu/drm/i915/Makefile | 1 -
> drivers/gpu/drm/i915/display/intel_display.c | 2 +-
> drivers/gpu/drm/i915/display/intel_dp.c | 1 +
> drivers/gpu/drm/i915/gem/i915_gem_mman.c | 2 +-
> drivers/gpu/drm/i915/gem/i915_gem_pages.c | 2 +-
> drivers/gpu/drm/i915/i915_gpu_error.c | 1 +
> 6 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index 91355c2ea8a5..8cace65f50ce 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -16,7 +16,6 @@ subdir-ccflags-y := -Wall -Wextra
> subdir-ccflags-y += $(call cc-disable-warning, unused-parameter)
> subdir-ccflags-y += $(call cc-disable-warning, type-limits)
> subdir-ccflags-y += $(call cc-disable-warning, missing-field-initializers)
> -subdir-ccflags-y += $(call cc-disable-warning, implicit-fallthrough)
> subdir-ccflags-y += $(call cc-disable-warning, unused-but-set-variable)
> # clang warnings
> subdir-ccflags-y += $(call cc-disable-warning, sign-compare)
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 8592a7d422de..30b97ded6fdd 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -12042,7 +12042,7 @@ static bool check_digital_port_conflicts(struct intel_atomic_state *state)
> case INTEL_OUTPUT_DDI:
> if (WARN_ON(!HAS_DDI(to_i915(dev))))
> break;
> - /* else: fall through */
> + /* else, fall through */
> case INTEL_OUTPUT_DP:
> case INTEL_OUTPUT_HDMI:
> case INTEL_OUTPUT_EDP:
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 4336df46fe78..d0fc34826771 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -231,6 +231,7 @@ static int intel_dp_get_fia_supported_lane_count(struct intel_dp *intel_dp)
> switch (lane_info) {
> default:
> MISSING_CASE(lane_info);
> + /* fall through */
> case 1:
> case 2:
> case 4:
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> index 391621ee3cbb..39a661927d8e 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> @@ -341,7 +341,7 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
> */
> if (!i915_terminally_wedged(i915))
> return VM_FAULT_SIGBUS;
> - /* else: fall through */
> + /* else, fall through */
> case -EAGAIN:
> /*
> * EAGAIN means the gpu is hung and we'll wait for the error
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> index b36ad269f4ea..65eb430cedba 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -268,7 +268,7 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj,
> switch (type) {
> default:
> MISSING_CASE(type);
> - /* fallthrough to use PAGE_KERNEL anyway */
> + /* fallthrough - to use PAGE_KERNEL anyway */
> case I915_MAP_WB:
> pgprot = PAGE_KERNEL;
> break;
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index b7e9fddef270..41a511d5267f 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1194,6 +1194,7 @@ static void error_record_engine_registers(struct i915_gpu_state *error,
> switch (engine->id) {
> default:
> MISSING_CASE(engine->id);
> + /* fall through */
> case RCS0:
> mmio = RENDER_HWS_PGA_GEN7;
> break;
> --
> 2.22.0
>

--
Kees Cook