Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> As a virtual engine may change the rq->engine to point to the active
> request in flight, we need to warn the compiler that an active request's
> engine is volatile.
>
> [ 95.017686] write (marked) to 0xffff8881e8386b10 of 8 bytes by interrupt on cpu 2:
> [ 95.018123] execlists_dequeue+0x762/0x2150 [i915]
> [ 95.018539] __execlists_submission_tasklet+0x48/0x60 [i915]
> [ 95.018955] execlists_submission_tasklet+0xd3/0x170 [i915]
> [ 95.018986] tasklet_action_common.isra.0+0x42/0xa0
> [ 95.019016] __do_softirq+0xd7/0x2cd
> [ 95.019043] irq_exit+0xbe/0xe0
> [ 95.019068] irq_work_interrupt+0xf/0x20
> [ 95.019491] i915_request_retire+0x2c5/0x670 [i915]
> [ 95.019937] retire_requests+0xa1/0xf0 [i915]
> [ 95.020348] engine_retire+0xa1/0xe0 [i915]
> [ 95.020376] process_one_work+0x3b1/0x690
> [ 95.020403] worker_thread+0x80/0x670
> [ 95.020429] kthread+0x19a/0x1e0
> [ 95.020454] ret_from_fork+0x1f/0x30
> [ 95.020476]
> [ 95.020498] read to 0xffff8881e8386b10 of 8 bytes by task 8909 on cpu 3:
> [ 95.020918] __i915_request_commit+0x177/0x220 [i915]
> [ 95.021329] i915_gem_do_execbuffer+0x38c4/0x4e50 [i915]
> [ 95.021750] i915_gem_execbuffer2_ioctl+0x2c3/0x580 [i915]
> [ 95.021784] drm_ioctl_kernel+0xe4/0x120
> [ 95.021809] drm_ioctl+0x297/0x4c7
> [ 95.021832] ksys_ioctl+0x89/0xb0
> [ 95.021865] __x64_sys_ioctl+0x42/0x60
> [ 95.021901] do_syscall_64+0x6e/0x2c0
> [ 95.021927] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_request.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 74169671afb5..c0df71d7d0ff 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -977,6 +977,8 @@ emit_semaphore_wait(struct i915_request *to,
> struct i915_request *from,
> gfp_t gfp)
> {
> + const intel_engine_mask_t mask = READ_ONCE(from->engine)->mask;
> +
> if (!intel_context_use_semaphores(to->context))
> goto await_fence;
>
> @@ -984,7 +986,7 @@ emit_semaphore_wait(struct i915_request *to,
> goto await_fence;
>
> /* Just emit the first semaphore we see as request space is limited. */
> - if (already_busywaiting(to) & from->engine->mask)
> + if (already_busywaiting(to) & mask)
> goto await_fence;
>
> if (i915_request_await_start(to, from) < 0)
> @@ -997,7 +999,7 @@ emit_semaphore_wait(struct i915_request *to,
> if (__emit_semaphore_wait(to, from, from->fence.seqno))
> goto await_fence;
>
> - to->sched.semaphores |= from->engine->mask;
> + to->sched.semaphores |= mask;
> to->sched.flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;
> return 0;
>
> @@ -1338,7 +1340,7 @@ __i915_request_add_to_timeline(struct i915_request *rq)
> i915_seqno_passed(prev->fence.seqno,
> rq->fence.seqno));
>
> - if (is_power_of_2(prev->engine->mask | rq->engine->mask))
> + if (is_power_of_2(READ_ONCE(prev->engine)->mask | rq->engine->mask))
> i915_sw_fence_await_sw_fence(&rq->submit,
> &prev->submit,
> &rq->submitq);
> --
> 2.20.1
>
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