[Intel-gfx] [RFC] drm/i915: GEM_WARN_ON considered harmful
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Thu Sep 20 14:30:09 UTC 2018
Ping!
Any comments here?
Main goal was to allow GEM_WARN_ON as a statement, plus also protect
uses in if statements, which there are some who I think don't expect the
branch to completely disappear.
Regards,
Tvrtko
On 07/09/2018 12:53, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>
> GEM_WARN_ON currently has dangerous semantics where it is completely
> compiled out on !GEM_DEBUG builds. This can leave users who expect it to
> be more like a WARN_ON, just without a warning in non-debug builds, in
> complete ignorance.
>
> Another gotcha with it is that it cannot be used as a statement. Which is
> again different from a standard kernel WARN_ON.
>
> This patch fixes both problems by making it behave as one would expect.
>
> It can now be used both as an expression and as statement, and also the
> condition evaluates properly in all builds - code under the conditional
> will therefore not unexpectedly disappear.
>
> To satisfy call sites which really want the code under the conditional to
> completely disappear, we add GEM_DEBUG_WARN_ON and convert some of the
> callers to it. This one can also be used as both expression and statement.
>
> From the above it follows GEM_DEBUG_WARN_ON should be used in situations
> where we are certain the condition will be hit during development, but at
> a place in code where error can be handled to the benefit of not crashing
> the machine.
>
> GEM_WARN_ON on the other hand should be used where condition may happen in
> production and we just want to distinguish the level of debugging output
> emitted between the production and debug build.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Matthew Auld <matthew.auld at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> ---
> Quickly put together and compile tested only!
> ---
> drivers/gpu/drm/i915/i915_gem.h | 4 +++-
> drivers/gpu/drm/i915/i915_vma.c | 8 ++++----
> drivers/gpu/drm/i915/intel_engine_cs.c | 8 ++++----
> drivers/gpu/drm/i915/intel_lrc.c | 8 ++++----
> drivers/gpu/drm/i915/intel_workarounds.c | 2 +-
> 5 files changed, 16 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
> index 599c4f6eb1ea..b0e4b976880c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.h
> +++ b/drivers/gpu/drm/i915/i915_gem.h
> @@ -47,17 +47,19 @@ struct drm_i915_private;
> #define GEM_DEBUG_DECL(var) var
> #define GEM_DEBUG_EXEC(expr) expr
> #define GEM_DEBUG_BUG_ON(expr) GEM_BUG_ON(expr)
> +#define GEM_DEBUG_WARN_ON(expr) GEM_WARN_ON(expr)
>
> #else
>
> #define GEM_SHOW_DEBUG() (0)
>
> #define GEM_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
> -#define GEM_WARN_ON(expr) (BUILD_BUG_ON_INVALID(expr), 0)
> +#define GEM_WARN_ON(expr) ({ unlikely(!!(expr)); })
>
> #define GEM_DEBUG_DECL(var)
> #define GEM_DEBUG_EXEC(expr) do { } while (0)
> #define GEM_DEBUG_BUG_ON(expr)
> +#define GEM_DEBUG_WARN_ON(expr) ({ BUILD_BUG_ON_INVALID(expr); 0; })
> #endif
>
> #if IS_ENABLED(CONFIG_DRM_I915_TRACE_GEM)
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 31efc971a3a8..82652c3d1bed 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -305,12 +305,12 @@ int i915_vma_bind(struct i915_vma *vma, enum i915_cache_level cache_level,
> GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
> GEM_BUG_ON(vma->size > vma->node.size);
>
> - if (GEM_WARN_ON(range_overflows(vma->node.start,
> - vma->node.size,
> - vma->vm->total)))
> + if (GEM_DEBUG_WARN_ON(range_overflows(vma->node.start,
> + vma->node.size,
> + vma->vm->total)))
> return -ENODEV;
>
> - if (GEM_WARN_ON(!flags))
> + if (GEM_DEBUG_WARN_ON(!flags))
> return -EINVAL;
>
> bind_flags = 0;
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index 10cd051ba29e..8dbdb18b2668 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -273,13 +273,13 @@ intel_engine_setup(struct drm_i915_private *dev_priv,
> BUILD_BUG_ON(MAX_ENGINE_CLASS >= BIT(GEN11_ENGINE_CLASS_WIDTH));
> BUILD_BUG_ON(MAX_ENGINE_INSTANCE >= BIT(GEN11_ENGINE_INSTANCE_WIDTH));
>
> - if (GEM_WARN_ON(info->class > MAX_ENGINE_CLASS))
> + if (GEM_DEBUG_WARN_ON(info->class > MAX_ENGINE_CLASS))
> return -EINVAL;
>
> - if (GEM_WARN_ON(info->instance > MAX_ENGINE_INSTANCE))
> + if (GEM_DEBUG_WARN_ON(info->instance > MAX_ENGINE_INSTANCE))
> return -EINVAL;
>
> - if (GEM_WARN_ON(dev_priv->engine_class[info->class][info->instance]))
> + if (GEM_DEBUG_WARN_ON(dev_priv->engine_class[info->class][info->instance]))
> return -EINVAL;
>
> GEM_BUG_ON(dev_priv->engine[id]);
> @@ -399,7 +399,7 @@ int intel_engines_init(struct drm_i915_private *dev_priv)
> err = -EINVAL;
> err_id = id;
>
> - if (GEM_WARN_ON(!init))
> + if (GEM_DEBUG_WARN_ON(!init))
> goto cleanup;
>
> err = init(engine);
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 19c9c46308e5..a274cc695fa2 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1681,7 +1681,7 @@ static int intel_init_workaround_bb(struct intel_engine_cs *engine)
> unsigned int i;
> int ret;
>
> - if (GEM_WARN_ON(engine->id != RCS))
> + if (GEM_DEBUG_WARN_ON(engine->id != RCS))
> return -EINVAL;
>
> switch (INTEL_GEN(engine->i915)) {
> @@ -1720,8 +1720,8 @@ static int intel_init_workaround_bb(struct intel_engine_cs *engine)
> */
> for (i = 0; i < ARRAY_SIZE(wa_bb_fn); i++) {
> wa_bb[i]->offset = batch_ptr - batch;
> - if (GEM_WARN_ON(!IS_ALIGNED(wa_bb[i]->offset,
> - CACHELINE_BYTES))) {
> + if (GEM_DEBUG_WARN_ON(!IS_ALIGNED(wa_bb[i]->offset,
> + CACHELINE_BYTES))) {
> ret = -EINVAL;
> break;
> }
> @@ -1730,7 +1730,7 @@ static int intel_init_workaround_bb(struct intel_engine_cs *engine)
> wa_bb[i]->size = batch_ptr - (batch + wa_bb[i]->offset);
> }
>
> - BUG_ON(batch_ptr - batch > CTX_WA_BB_OBJ_SIZE);
> + GEM_BUG_ON(batch_ptr - batch > CTX_WA_BB_OBJ_SIZE);
>
> kunmap_atomic(batch);
> if (ret)
> diff --git a/drivers/gpu/drm/i915/intel_workarounds.c b/drivers/gpu/drm/i915/intel_workarounds.c
> index 4bcdeaf8d98f..fb746c4b7c38 100644
> --- a/drivers/gpu/drm/i915/intel_workarounds.c
> +++ b/drivers/gpu/drm/i915/intel_workarounds.c
> @@ -941,7 +941,7 @@ struct whitelist {
>
> static void whitelist_reg(struct whitelist *w, i915_reg_t reg)
> {
> - if (GEM_WARN_ON(w->count >= RING_MAX_NONPRIV_SLOTS))
> + if (GEM_DEBUG_WARN_ON(w->count >= RING_MAX_NONPRIV_SLOTS))
> return;
>
> w->reg[w->count++] = reg;
>
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