Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> [ 25.025543] BUG: KCSAN: data-race in __i915_request_create [i915] / process_csb [i915]
> [ 25.025561]
> [ 25.025573] write (marked) to 0xffff8881e85c1620 of 8 bytes by task 696 on cpu 1:
> [ 25.025789] __i915_request_create+0x54b/0x5d0 [i915]
> [ 25.026001] i915_request_create+0xcc/0x150 [i915]
> [ 25.026218] i915_gem_do_execbuffer+0x2f70/0x4c20 [i915]
> [ 25.026428] i915_gem_execbuffer2_ioctl+0x2c3/0x580 [i915]
> [ 25.026445] drm_ioctl_kernel+0xe4/0x120
> [ 25.026459] drm_ioctl+0x297/0x4c7
> [ 25.026472] ksys_ioctl+0x89/0xb0
> [ 25.026484] __x64_sys_ioctl+0x42/0x60
> [ 25.026497] do_syscall_64+0x6e/0x2c0
> [ 25.026510] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 25.026522]
> [ 25.026532] read to 0xffff8881e85c1620 of 8 bytes by interrupt on cpu 2:
> [ 25.026742] process_csb+0x8d6/0x1070 [i915]
> [ 25.026949] execlists_submission_tasklet+0x30/0x170 [i915]
> [ 25.026969] tasklet_action_common.isra.0+0x42/0xa0
> [ 25.026984] __do_softirq+0xd7/0x2cd
> [ 25.026997] irq_exit+0xbe/0xe0
> [ 25.027009] do_IRQ+0x51/0x100
> [ 25.027021] ret_from_intr+0x0/0x1c
> [ 25.027033] poll_idle+0x3e/0x13b
> [ 25.027047] cpuidle_enter_state+0x189/0x5d0
> [ 25.027060] cpuidle_enter+0x50/0x90
> [ 25.027074] do_idle+0x1a1/0x1f0
> [ 25.027086] cpu_startup_entry+0x14/0x16
> [ 25.027100] start_secondary+0x120/0x180
> [ 25.027116] secondary_startup_64+0xa4/0xb0
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/intel_lrc.c | 2 +-
> drivers/gpu/drm/i915/i915_utils.h | 6 ++++++
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index a1d268880cfe..6266ef2ae6a0 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1316,7 +1316,7 @@ __execlists_schedule_out(struct i915_request *rq,
> * If we have just completed this context, the engine may now be
> * idle and we want to re-enter powersaving.
> */
> - if (list_is_last(&rq->link, &ce->timeline->requests) &&
> + if (list_is_last_rcu(&rq->link, &ce->timeline->requests) &&
> i915_request_completed(rq))
> intel_engine_add_retire(engine, ce->timeline);
>
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index 26f3a4a50b40..03a73d2bd50d 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -260,6 +260,12 @@ static inline void __list_del_many(struct list_head *head,
> WRITE_ONCE(head->next, first);
> }
>
> +static inline int list_is_last_rcu(const struct list_head *list,
> + const struct list_head *head)
> +{
> + return READ_ONCE(list->next) == head;
> +}
> +
> /*
> * Wait until the work is finally complete, even if it tries to postpone
> * by requeueing itself. Note, that if the worker never cancels itself,
> --
> 2.20.1
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