On Thu, 20 Sep 2018, Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> 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.
I've said before I don't like the conditional early returns vanishing
depending on config options, but I've been shot down. I think this patch
is an improvement.
BR,
Jani.
>
> Regards,
>
> Tvrtko
>
> On 07/09/2018 12:53, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>>
>> 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@xxxxxxxxx>
>> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
>> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
>> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
>> ---
>> 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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--
Jani Nikula, Intel Open Source Graphics Center
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