On 06.05.2021 21:13, Matthew Brost wrote:
> Implement a stall timer which fails H2G CTBs once a period of time
> with no forward progress is reached to prevent deadlock.
>
> Also update to ct_write to return -EDEADLK rather than -EPIPE on a
> corrupted descriptor.
broken descriptor is really separate issue compared to no progress from
GuC side, I would really like to keep old error code
note that broken CTB descriptor is unrecoverable error, while on other
hand, in theory, we could recover from temporary non-moving CTB
>
> Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 48 +++++++++++++++++++++--
> 1 file changed, 45 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> index af7314d45a78..4eab319d61be 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> @@ -69,6 +69,8 @@ static inline struct drm_device *ct_to_drm(struct intel_guc_ct *ct)
> #define CTB_H2G_BUFFER_SIZE (SZ_4K)
> #define CTB_G2H_BUFFER_SIZE (SZ_4K)
>
> +#define MAX_US_STALL_CTB 1000000
nit: maybe we should make it a CONFIG value ?
> +
> struct ct_request {
> struct list_head link;
> u32 fence;
> @@ -315,6 +317,7 @@ int intel_guc_ct_enable(struct intel_guc_ct *ct)
>
> ct->requests.last_fence = 1;
> ct->enabled = true;
> + ct->stall_time = KTIME_MAX;
>
> return 0;
>
> @@ -378,7 +381,7 @@ static int ct_write(struct intel_guc_ct *ct,
> unsigned int i;
>
> if (unlikely(ctb->broken))
> - return -EPIPE;
> + return -EDEADLK;
>
> if (unlikely(desc->status))
> goto corrupted;
> @@ -449,7 +452,7 @@ static int ct_write(struct intel_guc_ct *ct,
> CT_ERROR(ct, "Corrupted descriptor head=%u tail=%u status=%#x\n",
> desc->head, desc->tail, desc->status);
> ctb->broken = true;
> - return -EPIPE;
> + return -EDEADLK;
> }
>
> /**
> @@ -494,6 +497,17 @@ static int wait_for_ct_request_update(struct ct_request *req, u32 *status)
> return err;
> }
>
> +static inline bool ct_deadlocked(struct intel_guc_ct *ct)
> +{
> + bool ret = ktime_us_delta(ktime_get(), ct->stall_time) >
> + MAX_US_STALL_CTB;
> +
> + if (unlikely(ret))
> + CT_ERROR(ct, "CT deadlocked\n");
> +
> + return ret;
> +}
> +
> static inline bool ctb_has_room(struct intel_guc_ct_buffer *ctb, u32 len_dw)
> {
> struct guc_ct_buffer_desc *desc = ctb->desc;
> @@ -505,6 +519,26 @@ static inline bool ctb_has_room(struct intel_guc_ct_buffer *ctb, u32 len_dw)
> return space >= len_dw;
> }
>
> +static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
> +{
> + struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
> +
> + lockdep_assert_held(&ct->ctbs.send.lock);
> +
> + if (unlikely(!ctb_has_room(ctb, len_dw))) {
> + if (ct->stall_time == KTIME_MAX)
> + ct->stall_time = ktime_get();
> +
> + if (unlikely(ct_deadlocked(ct)))
> + return -EDEADLK;
> + else
> + return -EBUSY;
> + }
> +
> + ct->stall_time = KTIME_MAX;
> + return 0;
> +}
> +
> static int ct_send_nb(struct intel_guc_ct *ct,
> const u32 *action,
> u32 len,
> @@ -517,7 +551,7 @@ static int ct_send_nb(struct intel_guc_ct *ct,
>
> spin_lock_irqsave(&ctb->lock, spin_flags);
>
> - ret = ctb_has_room(ctb, len + 1);
> + ret = has_room_nb(ct, len + 1);
> if (unlikely(ret))
> goto out;
>
> @@ -561,11 +595,19 @@ static int ct_send(struct intel_guc_ct *ct,
> retry:
> spin_lock_irqsave(&ct->ctbs.send.lock, flags);
> if (unlikely(!ctb_has_room(ctb, len + 1))) {
> + if (ct->stall_time == KTIME_MAX)
> + ct->stall_time = ktime_get();
> spin_unlock_irqrestore(&ct->ctbs.send.lock, flags);
> +
> + if (unlikely(ct_deadlocked(ct)))
> + return -EDEADLK;
> +
likely, instead of duplicating code, you can reuse has_room_nb here
> cond_resched();
> goto retry;
> }
>
> + ct->stall_time = KTIME_MAX;
> +
> fence = ct_get_next_fence(ct);
> request.fence = fence;
> request.status = 0;
>
