[Intel-gfx] [PATCH] drm/i915/execlists: Mark up the racy access to switch_priority_hint

[Mika Kuoppala]

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

> [ 7534.150687] BUG: KCSAN: data-race in __execlists_submission_tasklet [i915] / process_csb [i915]
> [ 7534.150706]
> [ 7534.150717] write to 0xffff8881f1bc24b4 of 4 bytes by task 24404 on cpu 3:
> [ 7534.150925]  __execlists_submission_tasklet+0x1158/0x2780 [i915]
> [ 7534.151133]  execlists_submit_request+0x2e8/0x2f0 [i915]
> [ 7534.151348]  submit_notify+0x8f/0xc0 [i915]
> [ 7534.151549]  __i915_sw_fence_complete+0x5d/0x3e0 [i915]
> [ 7534.151753]  i915_sw_fence_complete+0x58/0x80 [i915]
> [ 7534.151963]  i915_sw_fence_commit+0x16/0x20 [i915]
> [ 7534.152179]  __i915_request_queue+0x60/0x70 [i915]
> [ 7534.152388]  i915_gem_do_execbuffer+0x3997/0x4c20 [i915]
> [ 7534.152598]  i915_gem_execbuffer2_ioctl+0x2c3/0x580 [i915]
> [ 7534.152615]  drm_ioctl_kernel+0xe4/0x120
> [ 7534.152629]  drm_ioctl+0x297/0x4c7
> [ 7534.152642]  ksys_ioctl+0x89/0xb0
> [ 7534.152654]  __x64_sys_ioctl+0x42/0x60
> [ 7534.152667]  do_syscall_64+0x6e/0x2c0
> [ 7534.152681]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 7534.152693]
> [ 7534.152703] read to 0xffff8881f1bc24b4 of 4 bytes by interrupt on cpu 2:
> [ 7534.152914]  process_csb+0xe7c/0x10a0 [i915]
> [ 7534.153120]  execlists_submission_tasklet+0x30/0x170 [i915]
> [ 7534.153138]  tasklet_action_common.isra.0+0x42/0xa0
> [ 7534.153153]  __do_softirq+0xd7/0x2cd
> [ 7534.153166]  run_ksoftirqd+0x15/0x20
> [ 7534.153180]  smpboot_thread_fn+0x1ab/0x300
> [ 7534.153194]  kthread+0x19a/0x1e0
> [ 7534.153207]  ret_from_fork+0x1f/0x30
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_lrc.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 3eb7adc4e057..9890d248749e 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1792,12 +1792,13 @@ timeslice(const struct intel_engine_cs *engine)
>  static unsigned long
>  active_timeslice(const struct intel_engine_cs *engine)
>  {
> -	const struct i915_request *rq = *engine->execlists.active;
> +	const struct intel_engine_execlists *execlists = &engine->execlists;
> +	const struct i915_request *rq = *execlists->active;
>  
>  	if (!rq || i915_request_completed(rq))
>  		return 0;
>  
> -	if (engine->execlists.switch_priority_hint < effective_prio(rq))
> +	if (READ_ONCE(execlists->switch_priority_hint) < effective_prio(rq))
>  		return 0;
>  
>  	return timeslice(engine);
> @@ -1814,8 +1815,11 @@ static void set_timeslice(struct intel_engine_cs *engine)
>  static void start_timeslice(struct intel_engine_cs *engine)
>  {
>  	struct intel_engine_execlists *execlists = &engine->execlists;
> +	int prio = queue_prio(execlists);

const would have suited in here.
Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

>  
> -	execlists->switch_priority_hint = execlists->queue_priority_hint;
> +	WRITE_ONCE(execlists->switch_priority_hint, prio);
> +	if (prio == INT_MIN)
> +		return;
>  
>  	if (timer_pending(&execlists->timer))
>  		return;
> @@ -5342,10 +5346,10 @@ void intel_execlists_show_requests(struct intel_engine_cs *engine,
>  
>  	if (execlists->switch_priority_hint != INT_MIN)
>  		drm_printf(m, "\t\tSwitch priority hint: %d\n",
> -			   execlists->switch_priority_hint);
> +			   READ_ONCE(execlists->switch_priority_hint));
>  	if (execlists->queue_priority_hint != INT_MIN)
>  		drm_printf(m, "\t\tQueue priority hint: %d\n",
> -			   execlists->queue_priority_hint);
> +			   READ_ONCE(execlists->queue_priority_hint));
>  
>  	last = NULL;
>  	count = 0;
> -- 
> 2.20.1
>
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