[Intel-gfx] [PATCH 1/3] drm/i915/gt: Mark up racy reads for intel_context.inflight

[Mika Kuoppala]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> When being used across multiple real engines inside a virtual engine,
> the intel_context.inflight is updated atomically, and so we must
> annotate the racy read from outside the owning context.
>
> [11142.482846] BUG: KCSAN: data-race in __execlists_submission_tasklet [i915] / __execlists_submission_tasklet [i915]
> [11142.482867]
> [11142.482878] write (marked) to 0xffff8881f257b5e0 of 8 bytes by interrupt on cpu 2:
> [11142.483107]  __execlists_submission_tasklet+0x1d33/0x2120 [i915]
> [11142.483336]  execlists_submission_tasklet+0xd3/0x170 [i915]
> [11142.483355]  tasklet_action_common.isra.0+0x42/0xa0
> [11142.483371]  __do_softirq+0xd7/0x2cd
> [11142.483384]  irq_exit+0xbe/0xe0
> [11142.483401]  do_IRQ+0x51/0x100
> [11142.483424]  ret_from_intr+0x0/0x1c
> [11142.483446]  do_idle+0x133/0x1f0
> [11142.483465]  cpu_startup_entry+0x14/0x16
> [11142.483483]  start_secondary+0x120/0x180
> [11142.483498]  secondary_startup_64+0xa4/0xb0
> [11142.483512]
> [11142.483528] read to 0xffff8881f257b5e0 of 8 bytes by interrupt on cpu 1:
> [11142.483755]  __execlists_submission_tasklet+0x14e/0x2120 [i915]
> [11142.483981]  execlists_submission_tasklet+0xd3/0x170 [i915]
> [11142.483999]  tasklet_action_common.isra.0+0x42/0xa0
> [11142.484014]  __do_softirq+0xd7/0x2cd
> [11142.484028]  do_softirq_own_stack+0x2a/0x40
> [11142.484046]  do_softirq.part.0+0x26/0x30
> [11142.484071]  __local_bh_enable_ip+0x46/0x50
> [11142.484299]  i915_gem_do_execbuffer+0x39c1/0x4e50 [i915]
> [11142.484528]  i915_gem_execbuffer2_ioctl+0x2c3/0x580 [i915]
> [11142.484546]  drm_ioctl_kernel+0xe4/0x120
> [11142.484559]  drm_ioctl+0x297/0x4c7
> [11142.484572]  ksys_ioctl+0x89/0xb0
> [11142.484586]  __x64_sys_ioctl+0x42/0x60
> [11142.484610]  do_syscall_64+0x6e/0x2c0
> [11142.484627]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

> ---
>  drivers/gpu/drm/i915/gt/intel_context_types.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index 11278343b9b5..0f3b68b95c56 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -45,8 +45,8 @@ struct intel_context {
>  
>  	struct intel_engine_cs *engine;
>  	struct intel_engine_cs *inflight;
> -#define intel_context_inflight(ce) ptr_mask_bits((ce)->inflight, 2)
> -#define intel_context_inflight_count(ce) ptr_unmask_bits((ce)->inflight, 2)
> +#define intel_context_inflight(ce) ptr_mask_bits(READ_ONCE((ce)->inflight), 2)
> +#define intel_context_inflight_count(ce) ptr_unmask_bits(READ_ONCE((ce)->inflight), 2)
>  
>  	struct i915_address_space *vm;
>  	struct i915_gem_context __rcu *gem_context;
> -- 
> 2.20.1
>
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