[Intel-gfx] [PATCH 5/5] drm/i915/execlsts: Mark up racy inspection of current i915_request priority

[Mika Kuoppala]

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

> [  120.176548] BUG: KCSAN: data-race in __i915_schedule [i915] / effective_prio [i915]
> [  120.176566]
> [  120.176577] write to 0xffff8881e35e6540 of 4 bytes by task 730 on cpu 3:
> [  120.176792]  __i915_schedule+0x63e/0x920 [i915]
> [  120.177007]  __bump_priority+0x63/0x80 [i915]
> [  120.177220]  __i915_sched_node_add_dependency+0x258/0x300 [i915]
> [  120.177438]  i915_sched_node_add_dependency+0x50/0xa0 [i915]
> [  120.177654]  i915_request_await_dma_fence+0x1da/0x530 [i915]
> [  120.177867]  i915_request_await_object+0x2fe/0x470 [i915]
> [  120.178081]  i915_gem_do_execbuffer+0x45dc/0x4c20 [i915]
> [  120.178292]  i915_gem_execbuffer2_ioctl+0x2c3/0x580 [i915]
> [  120.178309]  drm_ioctl_kernel+0xe4/0x120
> [  120.178322]  drm_ioctl+0x297/0x4c7
> [  120.178335]  ksys_ioctl+0x89/0xb0
> [  120.178348]  __x64_sys_ioctl+0x42/0x60
> [  120.178361]  do_syscall_64+0x6e/0x2c0
> [  120.178375]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [  120.178387]
> [  120.178397] read to 0xffff8881e35e6540 of 4 bytes by interrupt on cpu 2:
> [  120.178606]  effective_prio+0x25/0xc0 [i915]
> [  120.178812]  process_csb+0xe8b/0x10a0 [i915]
> [  120.179021]  execlists_submission_tasklet+0x30/0x170 [i915]
> [  120.179038]  tasklet_action_common.isra.0+0x42/0xa0
> [  120.179053]  __do_softirq+0xd7/0x2cd
> [  120.179066]  irq_exit+0xbe/0xe0
> [  120.179078]  do_IRQ+0x51/0x100
> [  120.179090]  ret_from_intr+0x0/0x1c
> [  120.179104]  cpuidle_enter_state+0x1b8/0x5d0
> [  120.179117]  cpuidle_enter+0x50/0x90
> [  120.179131]  do_idle+0x1a1/0x1f0
> [  120.179145]  cpu_startup_entry+0x14/0x16
> [  120.179158]  start_secondary+0x120/0x180
> [  120.179172]  secondary_startup_64+0xa4/0xb0
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_lrc.c   | 2 +-
>  drivers/gpu/drm/i915/i915_scheduler.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 20dd3c2cfa2f..3eb7adc4e057 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -293,7 +293,7 @@ static inline struct i915_priolist *to_priolist(struct rb_node *rb)
>  
>  static inline int rq_prio(const struct i915_request *rq)
>  {
> -	return rq->sched.attr.priority;
> +	return READ_ONCE(rq->sched.attr.priority);
>  }
>  
>  static int effective_prio(const struct i915_request *rq)
> diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
> index 52f71e83e088..af51810dc78c 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler.c
> +++ b/drivers/gpu/drm/i915/i915_scheduler.c
> @@ -321,7 +321,7 @@ static void __i915_schedule(struct i915_sched_node *node,
>  
>  		GEM_BUG_ON(node_to_request(node)->engine != engine);
>  
> -		node->attr.priority = prio;
> +		WRITE_ONCE(node->attr.priority, prio);

Ah the symmetry,

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

>  
>  		/*
>  		 * Once the request is ready, it will be placed into the
> -- 
> 2.20.1