Re: [Intel-gfx] [PATCH 2/3] drm/i915/uncore: fix race around i915->params.mmio_debug

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/07/2023 10:48, Jani Nikula wrote:
> Only check the conditions for unclaimed reg debug once to avoid locking
> problems when i915->params.mmio_debug changes between header and footer.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8749
> Cc: Lee Shawn C <shawn.c.lee@intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>   drivers/gpu/drm/i915/intel_uncore.c | 21 ++++++++++++---------
>   1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index a88aa342b623..dfefad5a5fec 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1925,27 +1925,26 @@ __unclaimed_previous_reg_debug(struct intel_uncore *uncore,
>   			i915_mmio_reg_offset(reg));
>   }
>   
> -static inline void
> +static inline bool __must_check
>   unclaimed_reg_debug_header(struct intel_uncore *uncore,
>   			   const i915_reg_t reg, const bool read)
>   {
>   	if (likely(!uncore->i915->params.mmio_debug) || !uncore->debug)
> -		return;
> +		return false;
>   
>   	/* interrupts are disabled and re-enabled around uncore->lock usage */
>   	lockdep_assert_held(&uncore->lock);
>   
>   	spin_lock(&uncore->debug->lock);
>   	__unclaimed_previous_reg_debug(uncore, reg, read);
> +
> +	return true;
>   }
>   
>   static inline void
>   unclaimed_reg_debug_footer(struct intel_uncore *uncore,
>   			   const i915_reg_t reg, const bool read)
>   {
> -	if (likely(!uncore->i915->params.mmio_debug) || !uncore->debug)
> -		return;
> -
>   	/* interrupts are disabled and re-enabled around uncore->lock usage */
>   	lockdep_assert_held(&uncore->lock);
>   
> @@ -2008,13 +2007,15 @@ __gen2_read(64)
>   #define GEN6_READ_HEADER(x) \
>   	u32 offset = i915_mmio_reg_offset(reg); \
>   	unsigned long irqflags; \
> +	bool unclaimed_reg_debug; \
>   	u##x val = 0; \
>   	assert_rpm_wakelock_held(uncore->rpm); \
>   	spin_lock_irqsave(&uncore->lock, irqflags); \
> -	unclaimed_reg_debug_header(uncore, reg, true)
> +	unclaimed_reg_debug = unclaimed_reg_debug_header(uncore, reg, true)
>   
>   #define GEN6_READ_FOOTER \
> -	unclaimed_reg_debug_footer(uncore, reg, true); \
> +	if (unclaimed_reg_debug) \
> +		unclaimed_reg_debug_footer(uncore, reg, true);	\
>   	spin_unlock_irqrestore(&uncore->lock, irqflags); \
>   	trace_i915_reg_rw(false, reg, val, sizeof(val), trace); \
>   	return val
> @@ -2112,13 +2113,15 @@ __gen2_write(32)
>   #define GEN6_WRITE_HEADER \
>   	u32 offset = i915_mmio_reg_offset(reg); \
>   	unsigned long irqflags; \
> +	bool unclaimed_reg_debug; \
>   	trace_i915_reg_rw(true, reg, val, sizeof(val), trace); \
>   	assert_rpm_wakelock_held(uncore->rpm); \
>   	spin_lock_irqsave(&uncore->lock, irqflags); \
> -	unclaimed_reg_debug_header(uncore, reg, false)
> +	unclaimed_reg_debug = unclaimed_reg_debug_header(uncore, reg, false)
>   
>   #define GEN6_WRITE_FOOTER \
> -	unclaimed_reg_debug_footer(uncore, reg, false); \
> +	if (unclaimed_reg_debug) \
> +		unclaimed_reg_debug_footer(uncore, reg, false); \
>   	spin_unlock_irqrestore(&uncore->lock, irqflags)
>   
>   #define __gen6_write(x) \

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko